MINEROLOGY - vsm.edu.in

DEPARTMENT OF CIVIL ENGINEERING

1 Engineering Geology Lab, VSM College Of Engineering

MINEROLOGY

Identification of rock forming minerals using Physical properties.

1. AIM:

The aim of experiments 1 to 4 is: To make you acquaint with Physical properties of minerals

and enable you to identify rock forming and ore forming with the help of these properties.

2. OBJECTIVES:

After completing these experiments you should be able to

Describe the different Physical properties of minerals

identify the different rock forming and ore forming with the help of these

properties

Describe the main characteristic features of minerals

Describe the uses of minerals.

3. MATERIALS:

Minerals specimen, streak plate, penknife, magnifying glass, bar magnet

4. PHYSICAL PROPERTIES OF MINERALS:

Some important Physical properties which help you in identifying minerals are described below.

5. COLOUR:

Most minerals have a distinctive color that can be used for identification. In opaque minerals, the

color tends to be more consistent, so learning the colors associated with these minerals can be

very helpful in identification. Translucent to transparent minerals have a much more varied

degree of color due to the presence of trace minerals. Therefore, color alone is not reliable as a

single identifying characteristic.



Minerals are of two types’ dark colored minerals and light colored minerals. The dark colored

minerals absorb white light completely and uniformly. Light colored minerals reflect white light

completely and uniformly.

6. STREAK:

Streak is the color of the mineral in powdered form. Streak shows the true color of the mineral.

In large solid form, trace minerals can change the color appearance of a mineral by reflecting the

light in a certain way. Trace minerals have little influence on the reflection of the small powdery

particles of the streak.

The streak of metallic minerals tends to appear dark because the small particles of the streak

absorb the light hitting them. Non-metallic particles tend to reflect most of the light so they

appear lighter in color or almost white.

Because streak is a more accurate illustration of the mineral’s color, streak is a more reliable

property of minerals than color for identification.

7. LUSTER:

Luster is the property of minerals that indicates how much the surface of a mineral reflects light.

The luster of a mineral is affected by the brilliance of the light used to observe the mineral

surface. Luster of a mineral is described in the following terms:

Metallic: The mineral is opaque and reflects light as a metal. Ex: galena, gold, silver.

Sub-metallic: The mineral is opaque and dull. The mineral is dark colored.

Non-metallic: The mineral does not reflect light like a metal.

Nonmetallic minerals are described using modifiers that refer to commonly known qualities.

Waxy The mineral looks like paraffin or wax. Vitreous The mineral looks like broken glass.

Pearly the mineral appears iridescent, like a pearl. Silky the mineral looks fibrous, like silk.

Greasy the mineral looks like oil on water. Resinous the mineral looks like hardened tree sap

(resin).Adamantine The mineral looks brilliant, like a diamond.



8. CLEAVAGE:

Cleavage is the tendency of minerals to break giving a smooth surface in certain known

directions giving more or less smooth faces according to internal structure of minerals.

Minerals tend to break along lines or smooth surfaces when hit sharply. Different minerals break

in different ways showing different types of cleavage.

Cleavage is defined using two sets of criteria. The first set of criteria describes how easily the

cleavage is obtained. Cleavage is considered perfect if it is easily obtained and the cleavage

planes are easily distinguished. It is considered good if the cleavage is produced with some

difficulty but has obvious cleavage planes. Finally it is considered imperfect if cleavage is

obtained with difficulty and some of the planes are difficult to distinguish.

The second set of criteria is the direction of the cleavage surfaces. The names correspond to the

shape formed by the cleavage surfaces: Cubic, rhombohedra, octahedral, dodecahedral, basal or

prismatic.

9. FRACTURE:

In some minerals there is little or no tendency to develop cleavage such a specimen minerals will

break in different fashions. The observations on the broken surface are its fracture. Fracture

describes the quality of the cleavage surface. Most minerals display either uneven or grainy

fracture, conchoidal (curved, shell-like lines) fracture, or hackly (rough, jagged) fracture.

10. Hardness

Hardness is one of the better properties of minerals to use for identifying a mineral. Hardness is a

measure of the mineral’s resistance to scratching. The Mohs scale is a set of 10 minerals whose

hardness is known. The softest mineral, talc, has a Mohs scale rating of one. Diamond is the

hardest mineral and has a rating of ten. Softer minerals can be scratched by harder minerals

because the forces that hold the crystals together are weaker and can be broken by the harder

mineral.

The following is a listing of the minerals of the Mohs scale and their rating:



1. Talc

2. Gypsum

3. Calcite

4. Fluorite

5. Apatite

6. Orthoclase Feldspar

7. Quartz

8. Topaz

9. Corundum

10. Diamond

11. TENACITY

Tenacity is the characteristic that describes how the particles of a mineral hold together or

resist separation. The chart below gives the list of terms used to describe tenacity and a

description of each term.

1) Conchoidal: the broken surface is smooth and curved

2) Even: the broken

12. SPECIFIC GRAVITY:

Specific Gravity of a mineral is a comparison or ratio of the weight of the mineral to the

weight of an equal amount of water. The weight of the equal amount of water is found by

finding the difference between the weight of the mineral in air and the weight of the mineral

in water.

13. CRYSTAL STRUCTURE:

Mineral crystals occur in various shapes and sizes. The particular shape is determined by the

arrangement of the atoms, molecules or ions that make up the crystal and how they are joined.

This is called the crystal lattice. There are degrees of crystalline structure, in which the fibers of

the crystal become increasingly difficult or impossible to see with the naked eye or the use of a

hand lens. Microcrystalline and cryptocrystalline structures can only be viewed using high

magnification. If there is no crystalline structure, it is called amorphous. However, there are very

few amorphous crystals and these are only observed under extremely high magnification.



IDENTIFICATION OF SOME ROCK-FORMING MINERALS IN HAND SPECIMENS

properties QUARTZ orthoclase plagioclase mica amphibole pyroxene

Form Massive Dodecahedral

crystals

Bladed,

fibrous

Foliated,

massive

hexagonal Prisms

striated

Colour Colour

less

Pale pink white Silvery

white

Dark

green

black

luster Vitreous Vitreous Vitreous pearly Sub

Vitreous

Vitreous

fracture conchoidal Uneven Uneven Uneven Uneven Uneven

cleavage Absent 2 sets at 90° 2 sets at

90°

Perfect 1

set

2 sets at

120°

2 sets

imperfect

hardness 7 6 6 2-3 5-6 5-6

Sp. gravity Medium Medium Medium Medium Medium Medium

Diagonistic

properties

No

cleavage,

fracture

cleavage

Colour

cleavage

Colour

Cleavage

flaky

form

cleavage

Colour

cleavage

Colour

properties olivine garnet kyanite talc beryl tourmaline

Form Massive Dodecahedral

crystals

Bladed,

fibrous

Foliated,

massive

hexagonal Prisms

striated

Colour Olive

green

Red blue white green black

luster Dull Vitreous Vitreous Vitreous Vitreous

fracture Uneven Uneven Uneven Uneven Uneven Uneven

cleavage Absent Absent 2 sets 1 set 1 set 2 sets poor

hardness 6-7 6.5-7.5 4-5 1 7-8 7.5

Sp. gravity Medium Medium Medium Medium Medium Medium

Diagonistic

properties

colour form form

colour

Hardness,

soapy feel

form

colour

form

colour



properties serpentine calcite dolomite Kaolinice

Form platy crystalline crystalline massive

Colour green white

trnsperent

white white

luster greasy Vitreous Vitreous earthy

fracture Uneven Uneven Uneven

cleavage none 3 sets

at(105°)

3 sets Indistinct

Sp. gravity 2.5 2.7 2.8 2.6

hardness 4-6 3 3-4 2

Diagonistic

properties

Colour form Form,

hardness,

cleavage,

vigorous

reaction to

acid

Form,

cleavage,less

reaction to acid

Luatre soft to

touch

IDENTIFICATION OF SOME ORE-FORMING MINERALS IN HAND SPECIMENS

properties Grapite sphalerite galena pyrite Chalco

pyrite

chomite

Form Massive crystalline Cubic

crystals

Cubic

crystals

Massive granular

Colour black Honey

brown

Lead gray yellow Brassy

yellow

black

Streak black brown Lead gray Greenish

black

Greenish

black

brown

luster greasy resinous metallic metallic metallic Sub

metallic

fracture indistinct indistinct - Uneven Uneven Uneven

cleavage indistinct 1 sets 3 sets at

90°

3 set 1 set

hardness 1-2 3-4 2-3 6-7 3.5-4 5-6

Sp. gravity low Medium High(7.5) High(5) High(4.1) High(5)

Diagonistic

properties

Marks

paper,

soils

hand

Streak

Colour

Sp.

gravity

Streak

Colour

Streak

Colour

Form

Colour

Streak



properties magnetite hematite bauxite pyrolusite magnesite

Form granular Massive pisolitie Massive Massive

Colour black steel gray gray black white

Streak black Cherry red white black white

luster metallic metallic earthy dull metallic

fracture Uneven Uneven Uneven Uneven Uneven

cleavage Absent Absent Absent indistinct indistinct

hardness 5-6 5-6 4 variable 4-5

Sp. gravity High(5.2) High(5.2) Medium(3) 4.5-5 High(4.1)

Diagonistic

properties

magnetic Streak Colour form Soils the

fingers

Form

Colour



PETROLOGY

Megascopic identification of common

1) Igneous rocks

2) Sedimentary rocks

3) Metamorphic rocks using physical properties

1. Igneous rocks (EXP.NO 5):

1. AIM :

The aim of this experiment -5 is to identify the common Igneous.

2. INTRODUCTION :

Igneous rocks are directly derived from magma. They are considered as primary

rocks formed by the process of differentiation, crystallization and solidification of

magma. Magma can be defined as a completely or partly molten liquid phase of rock

substance. When magma is erupted at the surface of earth, under favorable

circumstances, through the volcanic events, fissures, and fractures it is termed as lava.

3. MODE OF FORMATION:

Igneous rocks are divided into three main groups on basis of depth of crystallization

of magma or lava. This classification purely depends on the field relations of the rocks.

According to the field occurrence, the rocks can be studied as a) plutonic rocks that are

emplaced at great depth in the crust mantel, where the prevailing pressure and temperature

conditions are favorable for the development of coarse grained texture in these rocks. B)

hypabyssal intermediate rocks emplaced at shallow depths in the crust and exhibit medium

grained textures. C) Volcanic rocks are formed at the surface of the earth by eruption and

solidification of lava and exhibit fine grained texture.

Mineralogy: there are more than twenty rock forming minerals present in igneous rocks.

All the minerals are of primary one and are mostly confined to quartz feldspar,

feldspathoid, olivine, pyroxene, and amphibole and mica groups. These minerals are

grouped into two classes according to their color. This is supposed to be descriptive

classification of minerals.

a) Felsic class (light colored): quartz (and its polymorphs), feldspar(K-feldspar,

plagioclase feldspar, perthite, etc) feldspathoid (leucite, nepheline, sodalite, etc),



muscovite mica minerals are grouped in this class. These minerals are rich in K, Na and

Ca and Al.

b) Marfic class (dark colored): , olivine(and its two end members). pyroxene, (enstatite,

hepersthene, audite, diopside,aegirine, etc) amphibole(hornblende, riebecklite, etc)

c) Mica (biotite) are grouped in this class. These minerals are rich in Mg(but alkali-

pyroxenes’ and amphiboles contain high amount of Na)

d) Genetic classification: generally minerals can be classified into three classes and they

are essential, accessory, and secondary minerals.

Essential, and accessory minerals are put together to describe as primary one. These

minerals are from only in magmatic environment under favorable P & T conditions. Each

mineral has its own pressure and temperature to crystallize effectively from a melt

(magma or lava). Essential minerals are those whose presence is absolutely necessary in

naming a rock. ). Accessory minerals are those minerals found in trace amounts in a rock

mode and their presence or absence does not effect in naming of a rock. For example

apatite, magnetite, sphene and fluorite are accessory minerals in a granite rock. Sphene,

ilmenite, pyrope, garnet and chromite are accessory minerals in basic and ultra basic

rocks. Corundum is an important accessory mineral in a nepheline syenite rock.

Secondary minerals are derived from primary minerals by deuteric or metamorphic or

hydrothermal alteration. Chlorite, serpentine, garnet, kyanite, sillimanite, and a lusite

cordietite, scapolite, sericite, chalcedony, agate, concrenite and zeolite are important

secondary minerals.

4. STRUCTURE AND TEXTURES:

Structures are large scale feature that can be observed by naked eye. Igneous rocks

generally exhibited common Structures like vesicular, amygdolodial, columnar, flow

bands and pillow Structures in extrusive rocks, while graphic, porphyritic and

layering(sheet) in intrusive rocks.

Vesicular Structures are commonly seen in volcanic rocks (basalt, rhyolites etc) and they

are pores- like features that are developed at the time of solidification of lava. During the

time of solidification and crystallization of molten lava, the lava loses its gases and

volatiles into atmosphere and ultimately it turn into a solid rock with vesicles, pores and

cavities. Such forms are described as vesicular structures.



The pores, vesicles and cavities vesicular structures are filling with Secondary minerals

like quartz, calcite and zeolite by later hydrothermal process, such mineral forms are

called amygdolodial structure.

Columnar structures are commonly seen basaltic rocks and they are formed under sub-

aerial conditions. They are pillar like features with four, five or six sided prisms.

Flow bands are commonly exhibited by acidic lavas rather than basic lavas such as

rhyloties and trachytes are extremely viscous to form as flow bands under favorable

circumstances.

Pillow Structures are typically found in spilites, which are soda-rich basic lavas. They are

small ellipsoidal bodies with biconves outline. Such peculiar features were developed

under marine conditions.

Graphic micro structures are commonly seen in granite and pegmatite. These structures

are developed due to intergrowth between two minerals such as quartz and feldspar. In

the micro structures grey quartz forms needless, wedge shaped rods, which are enclosed

in a white mass of K-feldspar.

Texture of rock is described in terms of size shape and mutual relations between crystals

and glassy matter present in a rock. They comprise the following properties.

1) Crystallinity (degree of Crystallization) i.e. the relative proportion of glass and

Crystals.

2) Granularity (grain size) i.e. the absolute and relative size of crystals.

3) Crystals shape.

4) Mutual relations between crystals and fine grained ground mass or glassy matter

5. Crystallinity:

Crystallinity of rock is described by ratio between the relative proportion of glass and

crystals present in it. If a rock is fully composed of Crystals, then the rock is

described as holocrystalline, gabbro, granite, diorite and syenite are in holocrystalline

form. If a rock is composed 100 % glass is said to be holohyalline.



Obsidian, pitchstone, rhyolite and trachyte are in holohyalline form the intermediate

from between holocrystalline is termed as mero crylline or merohyalline. A

merocrystalline rock is composed of both glass and crystals with different

proportions. Many types of basalt are this type only.

6. Granularity:

Granularity of rock is represented as the absolute and relative size of crystals presents

in it. Based on absolute size of crystals. The Igneous rocks are grouped into 4 textural

classes.

1) Very coarse grained texture with 1 cm diameter of crystals e.g. pegmatite,

porphyritic granite etc. a very coarse grained rock thin section has only one

mineral grain or a part of mineral grain under the specific magnification

2) coarse grained texture with range between 1 cm to 5mm diameter of crystals; e.g.

granite, syenite, gabbro, etc. a coarse grained rock thin section has 3 or 4 grains

under the same magnification, which is used in the former case.

3) Medium grained texture with range between 5 mm to 1mm diameter of crystals;

e.g. a Medium grained rock thin section has 5 or 6 mineral grains under the same

magnification, which is used in the former cases.

4) Fine grained texture with 1 mm diameter of crystals e.g basalt, andesites etc.

Based on the relative size of crystals, the texture of Igneous rocks can be

described into equigranular and inequigranular.

In the equigranular texture, all crystals are approximately the same size. Dunite,

peridotite, pyroxenite and anorthosite exhibit equigranular texture and they

contain uniform size of grains of olivine, pyroxene and plagioclase feldspar.

In the inequigranular texture the crystals are dissimilar in size as some crystals are

bigger (phenocrysts) and some crystals are smaller. According to the mutual

relations between phenocrysts and ground mass, the inequigranular textures are of

many but few are described below.

a) Porphyritic texture: it is variety of inequigranular texture, in which the big

crystals are embedded in a Fine grained ground mass. Such textures are common

in many basalts and granites. If crystals occur as bunches or clots a grained

ground mass, then the resultant porphyritic texture is known as



glomeropoorphyrotic texture. This texture is common in glomeroporphyrotic

basalt.

Poikilitic texture: it is also a variety of inequigranular texture, in which small

crystals of one or different minerals are randomly oriented enclosed in a big

crystal of one mineral. The host crystal is known as an oikocryst and the enclosed

crystals are called as chadacrysts. This texture is common in olivine gabbro.

b) Ophitic texture: lath shaped plagioclase crystals are randomly enclosed in a

large anhedral augite crystal is said to be ophitic texture. Such texture is

commonly seen in dolerites.

7. shapes:

According to the. Shapes of crystals the 3 types of textural terms are distinguished

as euhedral, subhedral and anhedral.

a) Euhedral: this textural term is used for euhedral crystals of rock. If a crystal is

completely bounded by its characteristics faces, then it is said to be euhedral form.

Olivine, orthopyroxene, clinopyroxene, hornblende, apatite, tourmaline, zircon,

sphene etc. occurs as euhedral grain in different igneous rocks.

b) Subhedral: this textural term is used for Subhedral crystals of rock. if a crystal partly

bounded by its characteristics faces is said to be subhedral form. Feldspars,

felssphathoids, micas, amphiboles, pyroxenes etc. occurs as subhedral grain in

different igneous rocks.

c) Anhedral: this textural term is used for anhedral grain of rock. If a crystal totally

lacks of it characteristics faces is said to be anhedral form. Quartz occurs as anhedral

grain in many acidic grain igneous rocks.

Based on the shape of crystal, the equigranular textures are described as follows.

a) Pan Idiomorphic texture is rarely seen in rock such as lamprophyres, in which the

mineral grains are mostly subhedral.

b) HyPan Idiomorphic texture is commonly seen in many gabbroic, granite rocks, in

which the mineral are mostly subhedral.

c) Allotrimorphic texture is seen in quartz bearing felsites, aplites and in some

granite, in which the mineral are mostly anhedral.



SEDIMENTARY ROCKS

1. AIM :

The aim of this experiment -6 is to identify the common sedimentary rocks.

2. . MODE OF FORMATION:

The formation of sedimentary rocks is entirely different from the formation of igneous rocks and

metamorphic rocks. The sedimentary rocks are mainly formed in 3 ways.

i)by mechanical accumulation of loose sediment, in which all clastic(detrial) rocks are

formed by the compation of loose fragments under load pressure of overburden or

weight of overlying sediments in the sedimentary basin and it was further supplemented

by cememtation of clays. This process is called lithification. Breccias, conglomerate,

sand stone, shale, siltstone, and mudstone are described as clastic rocks formed by this

process.

ii) by chemical precipitation of solutions, in which nonclastic(chemical sediments) rocks

are formed by precipitation of corbonate solutions, silica and iron solutions from

seawater. Lime stone, iron stone, siderite, opal, chert and flint are described as non clastic

precipitated rocks.

iii) by accumulation of organic matters. in which many blogenic sedimentary rocks are

formed due to consolidation of organic remains under biochemical or biomechanical

process. Peat, coal, guano and other biogenic rocks are considered to be as organic

sedimentary rocks.

3. CLASSIFICATION:

Classification of sedimentary rocks is arbitrarily fixed and is limitless. It serves to

distinguish one rock from other and also maintains to reconstruct palaeo sedimentary

environments. It promotes to correlation of different stratigraphic units from one area

to another area.\

a) Genetic classification: sedimentary rocks can be classified into two main classes

based on their mode of formation.



i) clastic(detrital) sedimentary rocks: these rocks are formed by the

consolidation of loose fragments of minerals or rocky matter, which are

derived from pre-exiting rocks. Breccias, conglomerate, sand stone, shale,

siltstone, and mudstone are grouped in this class.

ii) Non clastic(chemical and organic sedimentary rocks): which are formed

by the precipitation of corbonate solutions or silica and iron solution or

Lime stone, dolomite Lime stone, iron stone, chert, Peat, coal,guano and

other biogenic rocks are grouped in this class. Some rocks represents

mixed parentase between clastic and non clastic origin and the resultant

rocks are to be mixed rocks such as calcareous sand stone, silious lime

stone etc.

iii) Rudaceous rocks: which are very coarse grained clastic( or terrigenous)

rocks made up of poorly sorted gravel, pebbles and cobbles. The grain size

of the sediments are usually greater than 2mm in diameter and the

resultant rocks are named as rudites. Rudites are of two kinds (a)

conglomerates (b) breccias. These two rock type are distinguished by their

grain shape such that the conglomerates are composed of rounded and

sub- rounded grains and the breccias are mainly composed of angular and

sub- angular grains.

iv) Arenaceous rocks: which are very coarse grained terrigenous rocks mainly

made up of well sorted clastic between 2mm and 0.06mm in diameter. The

rock mainly consists of quartz (sand) feldspar and with little clay. Based

on the mineralogical composition arenaceous rocks are named as

quartzites with 94% of quartz: sand stone with 90% of quartz; 10% of

feldspar and clay: arkose with 75% of quartz and 25% of feldspar and clay

and grey wacke with more clay mineral matter than clastic(detrritals).

b) Chemical classification: Non clastic rocks are too fine grained to recognize in the

specimen and in the microscope just because of this reason the rock are classified

on the basis of their chemical composition rather than grain size. Some of the

rocks are listed against to their minerals composition and chemical composition.

Rocks are listed against to their minerals and chemical composition.



Rock Mineral composition chemical composition

Lime stone Calcite CaCO3

Dolomite Lime stone Dolomite Calcite (Ca MG)2 CO3

Iron stone Siderite FeCO3

Chert Chert SiO2 OH

Coal Durain. vitrain C

Salt Salt NaCl

Gypsum Gypsum CaSO42H2O

4. STRUCTURE:

Sedimentary rocks exhibit a wide variety of structure, which are grouped into two

main classes.

i) Primary structure: which are formed at the time of lithification of Sediments

relative dating of state and also the correlation of strata?

ii) Secondary structure: which are developed after the formation of sedimentary

deposits. Tectonic structures of sedimentary rocks are one which belongs to

this category or class.

Structures are described as large scale features, which can be studied or seen better

in the field ( at the out crop) rather than in the laboratory or under the microscope.

Some of the important structure of sedimentary rocks are briefly furnished below.

a) Bedding or classification: it is characteristic Structural feature of

sedimentary rocks. It represents and unique sedimentation unit and

consists of several layers or lamination. A layers or lamina in the bedding

is distinguished from other by its color. Composition and appearance.

Each layer has 1 cm or less thickness of sediments, which lies parallel to

the bed or bedding plane. A bedding plane seperates one bed from other

with sharp contact or with a irregular surface plane.

It is Primary structure oftenly exhibited by greywacke sand stone.

Graded bedding is caused by turbidity current in the deep sea water.

Under which the sediments are suspended and settled by the function and



non function of turbidity currents. In a bed, the sediments are graded from

coarse at the bottom and fine at the top. This vertical gradation in grain

size is depicted in a given figure.

b) Cross bedding: It is Primary structure commonly seen in the Arenaceous

rocks. It is caused by shallow water currents or wind current. It has two

sets of laminations. One set of laminations is nearly horizontal and other

set is incline. This irregularity of sedimentation is due to change in

velocity and direction of currents. Cross bedding is useful both as an

identification of plaeocurrent direction and also a “way up” pointer in

sedimentary requences that have been greatly folded.

c) Ripple marks: Ripple marks are commonly seen in sand stones. They are

of undulating structure formed by the marine or fluvil or wind currents.

d) Petrified wood: it is a Secondary structure formed due to accumulation of

dead bodies of animals in the strata or rock. Most of shell structures bear

pelcipoda or brachiopoda valves.

5. IDENTIFICATION:

Sedimentary rocks are easily recognized in the field and also in the laboratory by seeing their

characteristic structural and textural features. in the field these rocks stand as stratifies layers

with different color composition and thickness. They are soft one when compared with Igneous

and metamorphic rocks and virtually bounded with cementing materials. Practically the rocks

can be studied in two ways in the laboratory (i)by megascopic (hand specimen description)

observation, and (ii) by microscopic ( thin section studies) observation.

megascopic observation: coarse grained Sedimentary rocks are easily identified in hand

specimen. In hand specimen, one can inspect the color, mineralogical composition and form

(structure and texture) of coarse grained rocks. The rocks like breccias, conglomerate, sand

stone, orthoquartizite and arkose have coarse and simple sediments to promate for the

recognition of the rock. Fine grained Sedimentary rocks like shale and lime stone are somewhat

posed some what difficult to recognize in hand specimen, but they are easily identified under the

microscopic.



METAMORPHIC ROCKS:

1. AIM:

The aim of this experiment -7 is to identify the common metamorphic rocks.

2. INTRODUCTION :

Metamorphic rocks are considered to be as Secondary rocks derived from pre-

existing rocks, such as Igneous and Sedimentary. they have been formed by partly or

completely recrystallization of primary (original) rocks like Igneous and Sedimentary,

which have suffered mineralogical and textural set up under the influence of drastic

(new) temperature and pressure. The new temperature and pressure are virtually raised

in the earth crust by means of tectonic movements, overburden of tremendous loads in

geosynclines and intensive igneous activity. These physical components are supposed to

be higher than those at Sedimentary basinal areas and lower than those at which the rock

melts.

The mineralogical and textural transformation (change) of the original rocks takes

place only in solid state. Such changes occur at the deeper depth of the crust; near the

fault or fracture zones and at or near the igneous intrusion. Rock transformation involves

in various process of solid-state recrystallization is said to be metamorphism.

3. MODE OF FORMATION:

According to field evidences, there are three main kinds of metamorphic rocks. They are

contact metamorphic rocks, dynamic metamorphic rocks and regional metamorphic

rocks. These three kinds of metamorphic rocks have been expressed wide diversity in

their mode of formation.

The contact metamorphic rocks occur at or near the contact of igneous intrusion and they

have limited aerial extent. They have formed in a zone of metamorphism, which is

surrounding an intrusion.

Metamorphic changes occurred due to supplied of heat to country rock by cooling of an

igneous intrusion. This process of metamorphism is known as “thermal metamorphism”.

Dynamic metamorphic rocks occur at or near the fault or fracture zones and they have

very limited aerial extent. They have formed under intrusive shearing stress.



Regional metamorphic rocks are related to depth zones of metamorphism and they have

larger aerial extent. They occur in variety of geological settings and are need not be

associated with igneous intrusion and fault or thrust zones. The regional metamorphic

rocks have been formed under high temperature and high pressure.these physical

conditions are originated at considerable depth of earth’s crust; where the original

Sedimentary or igneous rocks were thoroughly converted into metamorphic rocks and

resultant rocks have foliation and lineation features.

4. CLASSIFICATION:

Classification of metamorphic rocks is widely useful in the description and

nomenclature of the rocks. Because of this reason, one should know about the various

criteria which are helpful to the classification. Metamorphic rocks can be classified

by means of structural and textural criteria and mineralogical or chemical basis.

Metamorphic rocks are broadly divided into two groups (a) foliated and

(b) weakly or non foliated metamorphic rocks, based on structural and textural

criteria.

Foliated metamorphic rocks are characterized by preferred orientation of

phyllosilicate minerals, such mica, chlorites, serpentines etc. in these rocks, minerals

lie in a particular way of orientation, where they exhibit planer features. Muscovite

schist, biotite schist, chlorite schist and serpentines are typically named as foliated

metamorphic rocks. Some rocks have linear features due to arrangement of tabular

minerals like amphiboles, quartz and feldspars. Such minerals lie in a pressure

direction to give rise to lineation.

The Foliation and lineation features are commonly seen in gneisses. Various schists

and gneisses are described as Foliated metamorphic rocks.

non foliated metamorphic rocks are devoid of Foliation and lineation features and

they exhibit granulose or granoblastic texture. Equidimensional grains, polygonal

outlines, planer boundaries and triple junctions are common featuresof such rocks.

They include granulites, amphiboles, quartzites, marbles, hornflese, spotted states and

ecologites.



According to mineralogical basis the rocks names are prefixed by dominant minerals.

For example schist contains biotite-garnet schist, hornblende schist, serpentine in

serpentine, muscovite in muscovite schist, quartz in quartzite, calcite in marble etc.

5. MINERALOGY:

Minerals of Metamorphic rocks are directly or indirectly derived from those of igneous or

Sedimentary rocks or metamorphic rocks by metamorphic process. They are considered

to be as secondary Minerals and are the products of metamorphic reactions.

Many metamorphic reactions are incomplete during the evolution of various types of

metamorphic rocks and they give different metamorphic minerals at different stages of

conditions of Metamorphism. Minerals like albite, muscovite, chlotire, tremolite,

actinolite, lawsonite, and epidotes from at low pressure and low temperature conditions

(low grade Metamorphism). Sphene, almandine, staurolite, biotite, hornblende and

andesine plagioclase from at medium pressure and medium temperature conditions.

6. STRUCTURES/TEXTURES:

The structure of metamorphic rocks is distinctly demarked from those of igneous and

sedimentary rocks in the field and also in the laboratory by their characters tics foliation

and lineation features.

Metamorphic structures are secondary in nature and they form due to deformation of rock

masses occur at different levels of the earth crust. They tend to depend on the

composition of original rock, the type of metamorphic process and also on the site of

metamorphic environment. The structures are very much useful in the description of

rocks and for this reason; one should know at least the common and important structures,

which are described below.

Granulose structure:

This structure is commonly seen in high grade metamorphic rocks, such as

ecologite,granulite marbles quartites and hornfelses. In hand specimen, the structure

appears as fresh massive granular in form. It develops tomosic arrangement of

equidimensional mineral grains under recrystallization process, where the temperature

and uniform pressure are high.



Schistose structure:

This structure is commonly seen in foliated metamorphic rocks, such as mica, schist,

chlorite, schist, hornblende schist, kynate-sillimanate schist, phyllite, slate etc. it develops

due to parallel arrangement of flaky or foliaceous minerals. Schistose rocks have perfect

slaty cleavage or rock cleavage. Along those cleavage planes, the said rock easily splits

into pieces. The splitting behaviors of rock is known as schistosity of foliation.

Muscovite, chlorite, biotite, tremoloite, talc, actinolite, amphyllite, hornblende, serpentine

and other allied minerals are responsible for the formation of schistosity.

Gneissos structure:

This structure is common in high grade foliated and lineated metamorphic rocks, such as

gneiss, hornblende gneiss, khondalite, leptynite etc. in hand specimen, it appears as a

banded form and those bands are different colors, mineralogy and textures. Usually the

white band is rich in felsic minerals quartz feldspar and ,muscovite while the dark band is

rich in mafic minerals garnet, biotite, hornblende, pyroxene, epidote, and chlorite.

Typhomorphic or true metamorphic texture:

Typhomorphic texture are the true metamorphic texture formed by the complete

obliteration of original mineral constituents in a metamorphic rock. Such texture are

commonly seen in complete metamorphosed rock. The term blastic is used as suffix in

naming of true metamorphic texture. Such as porphyroblastic texture, granoblastic

texture,poikiloblastic texture.

1. porphyroblastic texture: it is non-foliated texture in which mineral grains are unequal in

size. The big grain is surrounded by small grain like in porphyritic textureof igneous

origin. Here the big grain is named as porphyroblast. For example, garnet occurs as a

porphyroblast in porphyroblastic texture of many metamorphosed basic rocks, such as

amphibolites.

2. poikiloblastic texture: it is also non-foliated texture, in which small grains are enclosed in

a big grain. Here the big grain is named as poikloblast. For example the sieved garnet

occurs as poikiloblast.



3. granoblastic texture: it is also non-foliated texture, in which builds up with

equidimensional grains. Such grains usually exhibit planar boundaries, triple junctions

and polygonal outlines. It is very common in hornfeles, quzrtzites an marbles.

MEGASCOPIC IDENTIFICATION OF SOME IGNEOUS ROCKS

Property Granite Gabbro Dolerite Basalt

Colour White/gray/pink Dark gray/black Dark

gray/black

Dark

gray/black

Mineral Quqrtz, Plagioclase, Plagioclase, Plagioclase,

composition orthoclase, mica,

hornblende

pyroxene ,

hornblende

pyroxene ,

hornblende

pyroxene ,

hornblende

Texture Coarse-grained Coarse-grained medium-

grained

fine-grained

Structure Massive,

compact

Massive,

compact

Massive,

compact

vesicular

Type plutonic plutonic hypabyssal volcanic

Mode of

occurrence

Hills, large

bodies

Dykes and sills Dykes and

sills

Trap rocks

(lava layers)

Constructional

use

Buildings,

monuments,

polished slabs

rly ballast

Embankments,

pavements

Rly ballast,

Buildings,

pavements

Road metal,

aggregates



MEGASCOPIC IDENTIFICATION OF SOME SEDIMENTARY ROCKS

Property Sand stone Shale Lime

stone

Conglomerate Laterite

Colour varies varies varies varies

Mineral Quqrtz, Clay mineral calcite Rounded rock clay

composition Feldspar

(minor)

dolomite Pebbles

cemented

Fe & Al

Texture Coarse-

grained

medium-

grained

fine-grained fine-

grained

Coarse-

grained

Structure stratified laminated compact Assorted

pebbles

porous

Mode of

occurrence

stratified stratified stratified As thin strata Residual

Constructional

use

monuments,

pavements

- Slabs, tiles Buildings Buildings



MEGASCOPIC IDENTIFICATION OF SOME METAMORPHIC ROCKS

Property quartizite marble slate schist Gneiss khondalite

Colour White/gray White/gray/pink varies varies varies Gray-

brown

Mineral Quqrtz, calcite Clay

mineral

Quqrtz,

mica,

Quqrtz, Quqrtz,

composition Feldspar,

mica,

dolomite Quqrtz,

mica,

hornblende Feldspar,

hornblende

Feldspar,

garnet

Texture Coarse-

grained

compact laminated coarse-

grained

Coarse to

medium

Coarse to

medium

Structure compact banded Slaty

cleavages

foliation

schistose Gneissic

banding

schistose

Source rock Sand stone Lime stone Shale Shale Granite Igneous

Constructional

use

Road

metal,

slabs,

blocks

Slabs,tiles Slabs,tiles Road

metal,

temples

Property charnockite

Colour Gray- Dark gray,bluish-gray

Mineral composition Quqrtz, Feldspar,hypersthene

Texture Medium- fine grained

Structure Banded/foliated

Source Igneous rock

Constructional use



STRUCTURAL GEOLOGY

Type-I: problems related to thickness of strata

Type-II : problems related to strike and dip

Type-III : bore hole problems

Type-I: problems related to thickness of strata(exp.n0.8)

AIM: To determine the given to thickness of strata by graphical method.

Introduction:

Thickness of a bed is the shortest distance between its upper and lower surfaces. In other words it

is the perpendicular drawn to both the surfaces and it is known as TRUE THICKNESS [TT]

When a vertical bore hole is sunk on the inclined beds, it reaches the upper and lower surfaces at

different levels. The difference is known as VERTICAL THICKNESS [VT]. When a bed is

exposed on the ground it is an outcrop. An inclined bed is outcropped on a horizontal ground, its

upper and lower surfaces are found parallel to each other. The distance between the two surfaces

(bedding planes) is called WIDTH OF OUTCROP [WO]. It is usually measured along the dip

direction. Dip of an inclined bed is always expressed by its direction [Dd] and amount of dip

[DA]

All these factors viz true thickness [TT],

vertical thickness [VT], width of outcrop [WO], dip direction [Dd] and amount of dip [DA] are

interrelated. When some of them are known, the other can be determined by graphical method. In

graphical method, figures are drawn to a conventional scale and solutions are obtained.

THICKNESS PROBLEMS:

Note: (1) the dip angle is equal to the angle between the true thickness and vertical thickness

(2) Vertical thickness is always greater than true thickness.

1. Type-I: Date given – W and D (A) +D (d)

To determine –TT and VT.

Example: a coal seam is exposed on horizontal ground. It dips 30° westward. Its width of

outcrop is 360 m. determine true thickness and vertical thickness.

Procedure: draw a horizontal line. Measure and mark AB equal to width of outcrop given.

Construct 30° angle westward at A and B. draw a perpendicular to the lower surface from A. it is

the true thickness= 180 m.



Draw a perpendicular to AB downwards from A. it cuts the lower surface at P.

Measure ad it is the vertical thickness = 120 m.

2. Type-II: Date given – W+D (d) + VT

To determine –TT + D (a)

Example: a coal seam is exposed on level ground. It dips northward. Its width of outcrop is

180 m. a bore hole sunk from its upper bedding plane touches the lower bedding plane at a

depth of 105 m. determine true thickness and amount of inclination.

Procedure: draw a horizontal line. Mark south-north Measure AB width of outcrop. Draw a

perpendicular at B downwards. Measure 105 mts, mark D, BD is vertical thickness, join AD

and extend downward. It is lower bedding plane. Draw upper bedding plane from B parallel to

AD. Draw perpendicular from B TO AD. It cuts AD at C. BC is true thickness. Measure BC =

90 m.

Measure dip angle BAD = 30°

3. Type-III: Date given – TT+D (a) + D (d)

To determine –VT + W

Example: on a horizontal tunnel, a bed of sand-stone dips 30° eastward. Its true thickness is

200 m. determine vertical thickness and width of outcrop in the tunnel.

Procedure: draw a horizontal line XY. Mark B point. Construct YBZ-30° dip angle eastward.

BZ is upper surface of sandstone. Draw perpendicular to BZ at B downward. Measure 200 mts,

mark C.BC is the true thickness, draw parallel to BZ from C. it cuts the XY line at A. Measure

AB = width of out crop = 400 m.

4. Type-IV: Date given – VT + Dip

To determine –TT + W

Example: a vertical bore hole sunk from the upper bedding plane of a shale bed reaches the

lower bedding plane at a depth of 150 m. it dips 35° westwards. Determine true thickness and

width of outcrop on level ground.

Procedure: draw a horizontal line XY. Mark A point. Construct XAZ-35° dip angle westward.

AZ IS The upper surfaces. Draw perpendicular to XY from A downward. Mark D point at a

depth of 150 m. draw parallel to AZ from D. it cuts the XY line at B. BD is lower bedding plane.

Measure AB=W=218 m.



Type-II: problems- strike and dip problems (Exp .No 9)

AIM: To determine the given to thickness of strata by graphical method.

Introduction:

In all inclined beds, dip and strike are co-existing and they are mutually perpendicular.

TRUE DIP is maximum amount of inclination and it is only one, which is always perpendicular

to strike direction. But dips are often measured in the adjacent direction of the true dip. They are

always less than the true dip. They are in between true dip and strike directions. Farther away

from the true dip direction, they become less and zero along the strike direction. Such dips are

known as APPARENT DIPS. They are many on either side of true dip.

Note: true dip apparent dips are interrelated. They can be determined from the available date

from the field or map. Dip and strike problems can be solved by graphical method.

1. Type-I:

Date known- 2 apparent dips - directions and amount.

To determine true dip, direction and amount.

Example: A bed of sandstone dips 30° along S 35°W and 38° along N 60°W. Determine its true

dip by graphical.

Procedure: draw north-south and east-west lines. Let them intersect O. describe a vector circle-

O its center with convenient radius (preferably 2.5 cm).

Draw OA along apparent dip S 35°W (AD1). draw a perpendicular to it at O. it intersects the

circle at R. construct complementary angle of the given apparent dips (90°-30°) 60° at P. it cuts

O at M . OMR=30°.

Similarly draw OB along apparent dip N 60°W (AD2). draw a perpendicular to it at O. IT cuts

the circle at P. construct complementary angle of the given apparent dips (90°-38°) 52° at P. it

cuts OB at Q. angle OQP=38° join MQ. It forms the true strike direction (TSD) to determine the

direction of true dip, draw a perpendicular to TSD from O. it cuts the TSD line at X; OX is the

direction of true dip. Measure angle SOX. It is S 85°W.

To determine the amount of true dip along OX draws a perpendicular to it at O. it cuts the circle

at Y, join XY. Measure angle OXY. It is 42°

TRUE DIP - 42° along S 35°W.

2. Type-II

Date given- TD (amount & direction)



AD1 (direction)

To determine AD (amount)

Example: A bed of shale is dipping maximum of 32° along SE. find the amount of its

inclination along S 80°E.


O. draw true dip directional line OP along SE. draw a perpendicular to OP at O. It cuts the circle

at A. construct complementary angle of true dips (90°-32°) 58° at A.. It cuts OP line at B. draw

a perpendicular to OP at B. it is strike direction (TSD).

Draw apparent dip direction line OQ. It cuts TSD line at Y. draw a perpendicular to OQ at O. it

cuts the circle at X join XY. Measure angle OXY=26°.

3. Type-III: Date given: TD+AD (amt)

To determine AD1 (direction).

Example: a coal seam is overlying sandstone and has a maximum dip of 42° towards south; two

inclined tunnels are proposed on the upper bedding plane of sandstone to have an inclination of

30°. Determine the direction of the tunnels.


O. Draw true dip directional line along OS. Draw a perpendicular to it at O. it intersects the

circle at P. Construct complementary angle of true dips (90°-42°) 48° at P.. it cuts OS line at Q.

draw a perpendicular to OS at Q. it is true strike direction (TSD).

To plot the direction of apparent dip, select arbitrarily any suitable direction. Let us take OE.

Draw perpendicular ON. It cuts the circle at X. construct the complementary angle of apparent

dip (90°-30°) 60° at X. it cuts OE line at Y. angle OYX is 30°.

With O as center and OY as radius, draw a circle to cut TSD at A and B. join OA and OB.

Measure angle SOA and angle SOB. They are S 50°W and S 50°E

. 4. Type-IV:

Date given: apparent dip- direction and amount, TD direction

To determine: T.D-amount.

Example: a coal seam has an apparent dip of 35° along S 35°E. The maximum dip is S 10°W.

Calculate the amount of true dip a coal seam.

Procedure: draw north-south and east-west lines. Let them intersect O. describe a vector circle

of 2.5 cm radius from O. draw apparent directional line OA along S 35°E . Draw a



perpendicular to it at O. . It cuts the circle at B. construct the complementary angle of apparent

dip (90°-35°) 55° at B. it cuts OA line at X.

Draw true dip directional line OC along S 10°W. Draw a perpendicular to OC-TD line from X. it

cuts OC at D. DX is true strike direction (TSD). Draw a perpendicular to OC at O. it cuts the

circle at E. join FD measure angle FDC. It is 44°.

Type-III: problems - borehole problems

Introduction:

In order to determine the subsurface geology of an area, boreholes are sunk at convenient

places. In areas such as cultivated lands, forests, deserts, alluvium etc the surface is completely

covered and outcrops are very few. Such boreholes reveal the presence of economic deposits of

coal, petroleum etc, the subsurface geological formations, rock types and their dip and strike can

be determined from such borehole data, which render very valuable information for planning for

exploiting the hidden treasures.

Example: three boreholes are sunk at 3 points of an equilateral triangle whose sides are 480m

each. P is west of Q and R is north of midpoint PQ. Boreholes P, Q and R reach the upper

surface of a rich coal seam at 100m, 220m and 260m depth respectively (a) determine the

attitudes (dip and strike) of the coal seam, (b) ) another borehole is sunk at S – midpoint of QR.

determine at what depth the borehole S reaches the same coal seam. If it is actually touches at

360m. Determine the geological structure. Scale 1Cm = 100m

Procedure:

Construct an equilateral triangle with a suitable scale. Show the position of the borehole.

The coal seam is reached at P and Q at 100m and 220m. so the coal seam dips from P to Q. To

determine the inclination along PQ construct rough sketch (a) depth diagram and determine the

gradient. It is 120m in 480m. So it is 1 in 4. Similarly construct depth diagram along PR. It is

160m in 480m i.e. 1 in 3. Take convenient scale and mark 4 units (cms) along PQ and 3 units

(cms) along PR from P. they are A and B join AB and extend. It is true strike direction (TSD).

Drop a perpendicular to AB from P. it cuts AB at C. measure PC. It is 2.85 cms i.e. the gradient

is 1 in 2.85. it is true dip.

To determine the direction of true dip, measure the angle CPQ = 45° SO the direction of true

dip is the complementary angle from north direction. So (90°-45°) 45°. So it is N 45°E.

True dip. - 1 in 2.85 along NE. strike – SE and NW.

. To determine the depth at which the borehole ‘S’ reaches the same coal seam, join PS. It

intersects AB line (true strike direction) at T. measure PT with units selected. It is 3cm. so the

gradient along PT is 1 in 3. Measure PS. It is 4.2 cm = 420m.



Depth = (horizontal distance PS x gradient) + depth of borehole at P.

= (420 X 1/3) + 100m

= 140m + 100m = 240m

Determine the geological structure: in the borehole ‘S’ the Depth calculated is 240mts. But it is

reaching the formation at 360mts, May indicative of faulting.

DETERMINATION OF GEOLOGICAL STRUCTURES:

Introduction:

In order to determine the subsurface geology of an area, boreholes are sunk at convenient places.

In areas such as cultivated lands, forests, deserts, alluvium etc the surface is completely covered

and outcrops are very few. Such boreholes reveal the presence of economic deposits of coal,

petroleum etc, the subsurface geological formations, rock types and their dip and strike can be

determined from such borehole data, which render very valuable information for planning for

exploiting the hidden treasures.

Example: three boreholes are sunk at 3 points of an equilateral triangle whose sides are 480m

each. P is west of Q and R is north of midpoint PQ. Boreholes P, Q and R reach the upper

surface of a rich coal seam at 100m, 220m and 260m depth respectively (a) determine the

attitudes (dip and strike) of the coal seam, (b) ) another borehole is sunk at S – midpoint of QR.

determine at what depth the borehole S reaches the same coal seam. If it is actually touches at

360m. Determine the geological structure. Scale 1Cm = 100m

Procedure:

Construct an equilateral triangle with a suitable scale. Show the position of the borehole.

The coal seam is reached at P and Q at 100m and 220m. so the coal seam dips from P to Q. To

determine the inclination along PQ construct rough sketch (a) depth diagram and determine the

gradient. It is 120m in 480m. So it is 1 in 4. Similarly construct depth diagram along PR. It is

160m in 480m i.e. 1 in 3. Take convenient scale and mark 4 units (cms) along PQ and 3 units

(cms) along PR from P. they are A and B join AB and extend. It is true strike direction (TSD).

Drop a perpendicular to AB from P. it cuts AB at C. measure PC. It is 2.85 cms i.e. the gradient

is 1 in 2.85. it is true dip.

To determine the direction of true dip, measure the angle CPQ = 45° SO the direction of true

dip is the complementary angle from north direction. So (90°-45°) 45°. So it is N 45°E.

True dip. - 1 in 2.85 along NE. strike – SE and NW.



. To determine the depth at which the borehole ‘S’ reaches the same coal seam, join PS. It

intersects AB line (true strike direction) at T. measure PT with units selected. It is 3cm. so the

gradient along PT is 1 in 3. Measure PS. It is 4.2 cm = 420m.

Depth = (horizontal distance PS x gradient) + depth of borehole at P.

= (420 X 1/3) + 100m

= 140m + 100m = 240m

Determine the geological structure: in the borehole ‘S’ the Depth calculated is 240mts. But it is

reaching the formation at 360mts, May indicative of faulting.



GEOLOGY MAP STUDY

1. AIM:

To draw the cross section of geological maps.

2. MATERIALS:

Geological map, white paper, pencil, eraser, scale, set squares.

3. PROCEDURE:

Draw a profile of the map along the straight line X-Y fig.

Place the paper strip (A-B) again on the X-Y line of the map, this time mark the points of

intersection of bedding planes on the edge of the paper strip shown in fig.

Now Place the paper strip again on the base of the profile so that the points X-Y on the

paper strip coincide with the X-Y of the profile as shown in fig

Now transfer all the bedding planes points of bedding planes marked on the paper to base

of the profile as shown in fig. and through them other perpendicular with dotted lines to

meet the profile.

All the beds in fig. are dipping at angle of a towards X, draw a straight line R-S inclined

to X-Y at an angle 0 towards X.

Now through ‘O’ and ‘P’ draw parallel line to RS as OO’ and PP’ at an angle 0 towards

X. and they are the bottom of the bed.

Name the beds as per their depositional order i.e. C---B- A as seen in the Geological

section. to Name the beds, proceed from ‘X’ to ‘Y’ or ‘Y’ to ‘X’ in map fig. if you are

walking from ‘Y’ to ‘X’ immediately after the point ‘Y’ you are stepping into the bed

‘C’, hence the bed in the section (fig) after the point ‘Y’ is the ‘C’ followed by ‘B’ and

the ‘A’ as shown in Geological section (figs 4a.1 – 4a.7)

STUDY AND INTERPRETATION:

1. AIM:

To study and interpretation of given geological maps.

2. MATERIALS:


3. PROCEDURE:

In the interpretation of geological section, when there are more than one series

present, younger beds must be drawn first, followed by the older. The older beds are



always projected to the base of the younger beds but not to the profile. Caution is

necessary in drawing the dip directions.

When the same bedding planes are repeated in a map it is necessary to calculate the

amount and directions of the dip as many times as the bedding planes are repeated.

The repetition of the bed may be an identification of the fold. It is evidenced by the

reversal of dip directions of the bedding planes.

An unconformity (a layer separating the older series of beds from the younger series)

may be identified in the map by truncation of the older series, i.e. against a line

(uniformity) the beds of older series are abruptly ending, where as the younger series

generally extend from one end of the map to the other end. When uniformity is

noticed in a map, calculate the amount and directions of the dip for older and younger

series. The unconformity in a Geological section is represented by a corrugated line

(…….)

Repetition of beds may be due to folding of the beds.

a) Repetition is due to folding, it is indicated by the reversal of dip direction of the

same bedding planes. It is due to fault it is recognized by a presence of a fault

line which may be a straight or curved (Note – the fault line should be treated as a

bed and its attitude is determined.)

b) If there is discontinuity of the against the fault line.

c) Some times change in the attitude of the beds on the other side of the fault plane.

d) Beds may be repeated or omitted

Recognition of horizontal, vertical beds in a geological map.

a) Horizontal beds: in a geological map when the bedding planes run parallel to the

contour lines the beds are horizontal (fig)

Note: when the beds are horizontal there is necessity of calculating dip. The beds in

profile are represented parallel to the line as shown in fig.

b) Vertical beds: the vertical beds in a geological map can be recognized by drawing the

strike line. When the strike lines are drawn, they pass one above the other, i.e. there will

not be any strike intervals shown in fig.

c)inclined beds are Recognized in a geological map, when the contour cut the bedding

planes there will be a strike interval and hence the beds will have inclination fig.

Note: when the strike interval increases dip decreases. when the strike interval decreases

dip increases.



COMPLETION OF OUT CROPS

1. AIM:

Completion of out crops.

2. MATERIALS:


3. PROCEDURE:

A geological map is shown.

X-Y is the reference line along which the profile has to be drawn.

Strike line: to draw a strike line select a bedding planes, this is intersected by the same

contour line at two points. For example the bedding planes are intersected by the 150mts

contour line at two points ’a’ and ‘b’. As these two points are at equal elevation, they are

joined and extended to the boundary of the map (MN) by a straight line. As the line is

drawn at the height of 150mts. The value of the strike line is also 150mts. So the line MN

is a strike line drawn for the A/B bedding planes A/B is now striking direction north-

south.

It is possible to drawn some more strike lines for the same bedding planes at other

elevation such as 100mts, 200mts, and 250mts. All these strike lines will be parallel to

each other because they were drawn at different elevation for the same bedding planes.

The perpendicular distance in fig measured between the two successive strike lines is the

strike interval.

Note: to draw a second strike lines if the bedding planes is intersected by the other

contour line only at the one place draw a parallel line to the first strike lines through that

single point of intersection. In the fig. a strike lines MN is drawn for the bedding planes

A/B because the bedding planes is intersected by the 250mts contour at the two points a

and b where as the strike lines OP is drawn parallel to MN through the point C which is

the only point of intersection between the bedding and where the bedding plane A/B is

intersecting contour at 200mts. Following with the above procedure you can draw the

strike lines for any given bed in a Geological map.

Dip : Dip is the inclination made by the bedding planes with the horizontal. The amount

of dip is calculated by knowing the strike interval and contour interval.



Contour interval

Dip= -----------------------------

Strike interval

Dip is also known by geometrical method where a right angle is constructed taking Strike

interval as the base and the Contour interval as the perpendicular to the base. The

procedure is as follows:

Draw two successive Strike lines for the same bedding plane

Measure the perpendicular distance (a-b) between the two successive Strike lines as

shown in fig. which gives the “Strike interval”

Note the interval between two contour lines are drawn as the Contour interval in fig. it is

50mts. Draw a straight line with a length equal to Strike interval as per the scale. In fig ab

is the Strike interval.

Draw a normal at ‘b’ or ‘a’ with a length equal to the Contour interval as per the scale. In

fig be represent the Contour interval.

Join ‘a’ and ‘c’ and measure the angle (bac) which is the amount of dip.

The directions of the dip is always perpendicular to the Strike from a higher Contour

value as indicated by arrows in fig. as there is a reference line X-Y, the directions of the

dip of the bed can be mentioned with reference to ‘X’, ‘Y’.

Note: as we are drawing a Geological section for the interpretation of the Geological

structure along the given reference line X-Y, the amount of dip calculated measuring the

Strike interval measured along the given reference line is perpendicular to the Strike line

(fig ‘ab’ along X-Y)

the amount of dip is true dip. When the Strike interval is measured (CD) along the

reference line X1-Y1 (FIG) is not perpendicular to the Strike line, the amount of dip is

“apparent dip”



UTILIZATION OF GEOLOGICAL MAPS TO PREPARE FEASIBILITY REPORT

FOR CIVIL ENGINEERING CONSTRUCTION WORKS/PROJECTS:

1. AIM:

Utilization of geological maps to prepare feasibility report for civil engineering construction

works/projects.

2. MATERIALS:


3. PROCEDURE:

In the interpretation of geological section, when there are more than one series

present, younger beds must be drawn first, followed by the older. The older beds are

always projected to the base of the younger beds, but not to the profile. Caution is

necessary in drawing the dip direction.

When the same bedding planes are repeated in a map it is necessary to calculate

the amount and direction. Of the dips many times as the bedding planes are repeated.

The repetition of the beds may be an identification of a fold. It is evidenced by the

reversal of dip direction of the same bedding planes.

An unconformity (a layer separating the older series of beds from the younger

series) may be identified in the map by truncation of the older series, i.e. against a

line (uniformity) the beds of older series are abruptly ending, where as the younger

series generally extend from one end of the map to the other end. When uniformity is

noticed in a map, calculate the amount and directions of the dip for older and younger

series. The unconformity in a Geological section is represented by a corrugated line

(…….)

Repetition of beds may be due to folding of the beds.

e) Repetition is due to folding, it is indicated by the reversal of dip direction of the

same bedding planes. It is due to fault it is recognized by a presence of a fault

line which may be a straight or curved (Note – the fault line should be treated as a

bed and its attitude is determined.)

f) If there is discontinuity of the against the fault line.

g) Some times change in the attitude of the beds on the other side of the fault plane.

h) Beds may be repeated or omitted

Recognition of horizontal, vertical beds in a geological map.

b) Horizontal beds: in a geological map when the bedding planes run parallel to the

contour lines the beds are horizontal (fig)



Note: when the beds are horizontal there is necessity of calculating dip. The beds in

profile are represented parallel to the line as shown in fig.

b) Vertical beds: the vertical beds in a geological map can be recognized by drawing the

strike line. When the strike lines are drawn, they pass one above the other, i.e. there will

not be any strike intervals shown in fig.

c)inclined beds are Recognized in a geological map, when the contour cut the bedding

planes there will be a strike interval and hence the beds will have inclination fig.

Note: when the strike interval increases dip decreases. when the strike interval decreases

dip increases. By means of above observation the feasibility report is prepared for a given

project.

Date post:	22-Dec-2021
Category:	Documents
Upload:	others
View:	2 times
Download:	0 times

MINEROLOGY - vsm.edu.in

Documents