Earth Materials

Rocks and Minerals

Minerals inorganic solidschemical composition

compoundsatoms joined together individual elements

ex. gold (Au), sulphur (S) two or more elements

ex. halite (NaCl)

Periodic Table of the Elements

Minerals, cont. Most of the common minerals are made of crystals What cause that crystalline characteristic?

regular arrangement of the compounds.

Mineral Propertiesuseful for identificationcolor

some mineral types occur in many colors streak: color of mineral powder

Mineral Properties, cont. luster

metallic vs. nonmetallic hardness

ability or resistance to scratching Moh scale (1 to 10)

1 is softest; 10 is hardest

• In 1822 a German scientist by the name of Frederick Mohs set up a scale to determine the approximate hardness of minerals.

Mineral Properties, cont. cleavage

whether or not mineral split or crack along parallel or flat planes These planes along which the mineral breaks are called cleavage

planes. If the mineral splits easily along these planes the mineral is then

said to have perfect cleavage .

Mica is a good example of perfect cleavage. Quartz shatters likes glass when struck with a hammer – No cleavage

Mineral Properties, cont.density

weight per unit volumecrystalline patternsmiscellaneous properties

ex. talc has a distinctive feel

Mineral TypesSilicates

contains mainly compounds of silicon and oxygenmay also contain metallic elements such

as iron or magnesium 75% of Earth’s minerals

quartz

Mineral Types, cont.nonsilicates

remaining 25% variety of types

native elements ex. Copper: Cu

combination of elements ex. Carbonates Calcite: CaCO3 Dolomite: CaMg(CO3)2

What eight elements make up over 98% of the Earth's

crust?

Note: They are, in decreasing quantity as you read downward

The Geologic Cycle

Figure 11.5

RocksMostly composed of a

combination of minerals

ore deposit large concentration of

an individual mineral

Rocks Cycle

The rock cycle represents the alteration of rock-forming minerals above and below the Earth's surface.

three categories of rocks igneous sedimentary Metamorphic

How they transform?

Igneous RocksFrom Latin word : “ignis” or fire

Forms from the cooling and crystallization of magma or lava Two main classification schemes:

a) texture b) chemistry Classes by texture

1. Extrusive Igneous rock Forms at the earth’s surface as lave cools

ex. Basalt (dark, fine grained) - Pumice (full of holes) , Obsidian (glassy)—pg 335

2. Intrusive Igneous rock/Plutonic rocks Forms deep underground where magma cools slowly. have a coarse, crystalline texture

ex. granite

Classified by Chemical composition

Felsic Word derived from Feldspar and Silica High in silica (65% + Usually light colored Ex. Rhyolite (extrusive) Granite (intrusive)

Mafic Word derived from Magnesium and Ferric (iron) Low silica content (45-55% or so) Usually dark-colored Examples: Basalt (extrusive) and Gabbro (intrusive)

In some text : You may find more divisions based on chemical composition: Intermediate , Ultramafic

Note: Silica is Silicon dioxide (SiO2)

Pluton

Figure 11.7

1. Any intrusive igneous rock can be further divided by size and orientation

-Batholith-Laccolith-Dike-Sill

Sedimentary Rocks derived from preexisting rocks, or from organic materials The exogenic processes of weathering and erosion generate the material sediments needed to form these rocks.

deposition, compaction, and cementation

CATEGORIES: 3 categories

1. Detrital/ Clastic ex. conglomerate, sandstone

Sedimentary Rocks, cont.

2. chemical types precipitated from water

ex. Rock salt (halite) limestone (calcium carbonate)

3. biochemical (organic) types ex. coal

Metamorphic Rocks Rocks altered in their physical and/or chemical composition by intense heat and/or pressure Metamorphism involves the transformation of a pre-existing rock to form new minerals and textures.

Preexisting rock Metamorphic Rock plutonic rocks gneiss

Metamorphic Rocks, cont

Pre-existing rock Metamorphic Rock shale slate

Metamorphic Rocks, cont Pre-existing rock Metamorphic Rock slate schist

Gneiss

Metamorphic Rocks, cont Pre-existing rock Metamorphic Rock limestone marble

Metamorphic environments & Processes Metamorphism occur by two processes:

(1) contact metamorphism a magma intrusion bakes or recrystallizes rock in a localized

area) occurs under low to moderate pressure and low to high

temperature conditions Temperatures -- vary widely from 400-1000°C.

Or…(2) regional metamorphism

where large scale deformation occurs from large scale compression or heating in areas.

METAMORPHIC ROCKS TYPES Meta. rocks broken down into 2 groups:

1. Foliated metamorphic rocks Usually associated with regional metamorphism Creates rocks with minerals

in distinct bands Most commonly occur at boundary of tectonic plates directed pressure

flattens and lengthens the rock in the direction of greatest pressure Examples of foliated meta. rocks = gneiss & slate.

Non-foliated metamorphic rocks Usually associated with contact Lack banding of minerals Largely occurs formed by Burial metamorphism in deep basins Examples of non-foliated metamorphic rocks are :

marble quartzite.

Quartzite