Warm-up

• What is the difference between a mineral and a rock?

• What properties can we use to identify minerals?

MineralsThe Building

Blocks of Rocks

Minerals - The Building Blocks of Rocks o Recall from chemistry that elements

and compounds are collectively known as “substances.”

o Elements bond together to form “compounds.”

o Elements and compounds have a definite chemical formula.o ex.) Elements: Na is sodium and Cl is

chlorine.o ex.) Compound: NaCl is sodium

chloride, or common table salt.o In geology, we normally call rocky

elements and compounds “minerals.”o Sodium chloride is called rock salt, or

halite, when we’re discussing minerals.

Figure 2.2

Minerals - The Building Blocks of Rocks A mineral is a naturally occurring solid chemical

substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical

properties.By comparison, a rock, which we will study later, is

an mixture of minerals and/or mineraloids and does not have a specific chemical composition.

Minerals range in composition from pure elements and simple salts to very

complex silicates with thousands of known forms.The study of minerals is called mineralogy.

Figure 2.3

Minerals - The Building Blocks of Rocks A mineral is naturally

occurring, inorganic, solid in phase, possesses an

orderly internal structure of atoms, and has a

definite chemical composition.

Mineraloids, on the other hand, lack an orderly

internal structure.

Lechatelierite

Fluorite

Minerals - The Building Blocks of Rocks

Physical properties of minerals

ColorThe color of a mineral is one of its most

obvious attributes, and is one of the properties that is always given in any

description. Color results from a mineral’s chemical composition,

impurities that may be present, and flaws or damage in the internal

structure. Color in minerals is caused by the absorption, or lack of absorption, of

various wavelengths of light.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Streak

When you rub a mineral on a flat surface, the color of the powder left behind on the

streak plate is the mineral's streak.

The streak and color of some minerals are the same. For others, the streak may be

quite different from the color.

Although the color of a mineral may not be very helpful in identification, the streak, which is the color of the

powered mineral, can be very useful.

Minerals - The Building Blocks of Rocks Physical properties of

mineralsFeel

Some specimens of a particular mineral may have a rough feel since they are composed of

tiny, protruding crystals, while other specimens of the same mineral have a smooth texture.Therefore, a rough feel is not necessarily an

identification factor.A greasy and smooth feel, however, are inherent

to all specimens of the same mineral.Fibrous minerals have a distinct, silky feel.

Minerals - The Building Blocks of Rocks

Physical properties of minerals

HardnessMineral hardness is based on

the ability of one natural sample of matter to scratch

another.Diamond is the hardest

known naturally occurring substance, whereas talc is the

least hard.

Minerals - The Building Blocks of Rocks

Physical properties of minerals

HardnessThe hardness of a material is

measured against the Mohs scale by finding the hardest material that

the given material can scratch, and/or the softest material that can scratch the given material.

For example, if some material is scratched by apatite but not by

fluorite, its hardness on the Mohs scale would fall between 4 and 5.

Figure 2.13

Mohs Scale of Hardness

Minerals - The Building Blocks of Rocks

Physical properties of minerals

CleavageIn mineral terms, cleavage describes how a crystal breaks when subject to

stress on a particular plane.If part of a crystal breaks due to stress and the broken piece retains a smooth plane or crystal shape, the mineral has

cleavage.A mineral that never produces any

crystallized fragments when broken off due to stress has no cleavage.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Habit

Mineral habit is the shape of how a mineral tends to form.

Types of mineral habits include columnar, blocky,

acicular (needle-like), granular, lamellar or foliated

(sheets easily split apart), botryoidal (like a bunch of

grapes), fibrous, radiating, or dendritic (like a fern).

The mineral quartz often exhibits good crystal shape

Pyrite (fool’s gold) has two common crystal forms

Figure 2.11

Figure 2.12Abladed habit

Figure 2.12Bprismatic habit

Figure 2.12Cbanded habit

Figure 2.12Dbotryoidal habit

Minerals - The Building Blocks of Rocks Physical properties

of minerals Luster

The luster of a mineral is the way its surface reflects light. In simplest

terms, minerals have a metallic or non-metallic luster. A metallic luster is a shiny, opaque appearance similar to

a bright chrome bumper on an automobile. Other shiny, but

somewhat translucent or transparent lusters (glassy, adamantine), along

with dull, earthy, waxy, and resinous lusters, are grouped as non-metallic.

The freshly broken sample of galena (right) displays a metallic luster, while the sample on

the left is tarnished and has a submetallic luster.

Minerals - The Building Blocks of Rocks Physical properties of

minerals Fracture

Fracture is a description of the way a mineral tends to break. It is different

from cleavage and parting, which are generally clean flat breaks along specific directions.

Different minerals will break in different ways and leave a surface that can be described in a recognizable way. Is the broken area smooth?

Irregular? Jagged? Splintery? These are some of the ways of describing fracture. Although many

minerals break in similar ways, some have a unique fracture and this can be diagnostic.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Fracture

The most common fracture type is conchoidal. This is a smoothly curved fracture that is familiar to

people who have examined broken glass. Sometimes described as

a clam-shell fracture. Quartz has this fracture type and almost all

specimens that have been broken, demonstrate this fracture type very

well.

Conchoidal Fracture

Figure 2.16

Minerals - The Building Blocks of Rocks Physical properties

of minerals Fracture

Uneven is a type that is basically self

explanatory. It is a common type that is found in anhydrite.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Fracture

Jagged fractures have sharp points or edges that

catch on a finger that's rubbed across the surface.

Usually this indicates a metal such as copper , a

metal alloy or some sulfides or oxides.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Fracture

Splintery is a fracture type that occurs in fibrous or finely acicular minerals and in minerals that have

a relatively stronger structure in one direction than the other two. Chrysotile serpentine is a typical mineral with splintery fracture, and kyanite is an example of a

non-fibrous mineral that has this fracture.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Fracture

Earthy is a fracture that produces a texture similar to broken children's clay.

It is found in minerals that are generally massive and loosely consolidated such

as limonite.

Minerals - The Building Blocks of Rocks Physical properties

of minerals Specific Gravity

Specific Gravity is a measure of the density of

a mineral. At times it is such a useful property

that it is the only way to distinguish some minerals

without laboratory or optical techniques.

Minerals - The Building Blocks of Rocks Physical properties of

minerals Specific Gravity

Gold an easily be distinguished from "fool's gold" by specific gravity alone

Specific gravity is a unit-less measure, because it is derived from the density of

the mineral divided by the density of water and thus all units cancel. However, since water's density equals 1 gram per cubic centimeter (at specific conditions),

then a mineral's specific gravity would also correspond to a mineral's density as

expressed in grams per cubic centimeter.

Minerals - The Building Blocks of Rocks Physical properties of

minerals Taste

Taste is not the first property someone would associate with minerals, yet taste is sometimes a very good characteristic and a key to identification in some cases. The

most commonly "tasted" mineral is halite or rock salt, but there are several

other minerals that have a distinctive taste.

• NOTE: Consult your instructor or a professional before tasting a mineral – some are poisonous!

Examples: Borax (sweet alkaline),

halcanthite (sweet metallic & slightly poisonous),

Epsomite (bitter), Glauberite (bitter salty),

Halite (salty), Hanksite (salty),

Melanterite (sweet, astringent and metallic),

Sylvite (bitter), Ulexite (alkaline)

Minerals - The Building Blocks of Rocks Physical properties of

minerals Smell

Several minerals give off a distinctive odor in certain conditions. Sulfur, in normal room

conditions, gives off a mild odor resembling the smell of a lighting match. However if

heated or struck, it gives off a powerful odor like rotten eggs. Arsenic gives off a very mild

garlic smell in normal room conditions. However, if heated or struck, it gives off a powerful garlic odor. Although only few

minerals have a characteristic odor, odor is very useful identification key.

Minerals - The Building Blocks of Rocks Physical properties of

mineralsTenacity – Brittleness

If a mineral is hammered and the result is a powder or small

crumbs, it is considered brittle.Brittle minerals leave a fine

powder if scratched, which is the way to test a mineral to see if it is

brittle.The majority of all minerals are

brittle.Minerals that are not brittle may

be referred to as non-brittle minerals.

Minerals - The Building Blocks of Rocks Physical properties of

mineralsTenacity – Sectility

Sectile minerals can be separated with a knife

into thin slices, much like wax.

Minerals - The Building Blocks of Rocks Physical properties of

mineralsTenacity – MalleabilityIf a mineral can be

flattened by pounding with a hammer, it is

malleable.All true metals are

malleable.

Minerals - The Building Blocks of Rocks Physical properties of

mineralsMagnetism

Several minerals react when placed within a magnetic field. Some minerals are strongly attracted to the magnet, others are weakly attracted, and one

mineral is repelled. There are also several minerals that are attracted to

magnetic fields only when heated.The presence of iron in a mineral is

responsible for the magnetic properties of minerals in virtually all cases.

Minerals - The Building Blocks of Rocks Physical properties

of mineralsDouble Refraction

Double refraction is a phenomenon exhibited on all non-

opaque minerals except for amorphous ones and ones that crystallize in the isometric system.A light ray enters the crystal and splits up into two separate rays,

making anything observed through the crystal appear as double.

Minerals - The Building Blocks of Rocks Physical properties

of mineralsDouble RefractionIn some minerals, such as

the Iceland Spar variety of Calcite, double refraction is strongly seen.

The double refraction is different in every mineral, and thus can be

used to identify gems.

Double refraction is measured with a refractometer.

Minerals - The Building Blocks of Rocks Physical properties of

mineralsReaction to Hydrochloric Acid An important property in minerals is how they

react to acids.All of the minerals that have some reaction to acids tend to be carbonates and a few other minerals that contain significant amounts of

carbonate ions.Carbon dioxide gas is given off.The bubbles or effervescence is

the reaction we are looking for and indicates the presence of carbonate ions.

Minerals - The Building Blocks of Rocks Physical properties

of mineralsReaction to

hydrochloric acid With calcite and aragonite, the two most common carbonate

minerals, the reaction to a cold, dilute acid is easily accomplished and is often so energetic that it is

associated with a fizzing noise.

The Rock-Forming MineralsThe eight elements that compose most

rock-forming minerals are oxygen (O), silicon

(Si), aluminum (Al), iron (Fe), calcium (Ca),

sodium (Na), potassium (K), and magnesium (Mg).

The most abundant atoms in Earth’s crust are oxygen (46.6% by

weight) and silicon (27.7% by weight)

Composition of the Continental Crust