Regents Earth Science – Unit 10: Minerals and RocksMinerals

A mineral is any:

1. naturally occurring

2. inorganic

3. solid, with a

4. definite chemical composition, and a

5. crystal structure

Examples:

1. naturally occurring: quartz, pyrite

• cement is not a mineral - man made

2. inorganic: not formed from living things

• coal is not a mineral - comes from plants

3. solid: have definite size/volume and shape

• oil is not a mineral - liquid

4. chemical composition: ex.: quartz = SiO25. crystal structure: atoms in geometric patterns

• ex.: quartz - silicon tetrahedronMinerals are classified into different groups based on their composition/structure:

• groups include: native elements, oxides, carbonates, halides, sulfides, and silicates

• ex.: native elements = silver, gold, graphite (C)

oxides = hematite, magnetite

carbonates = calcite, dolomite

halides = halite, flourite

sulfides = pyrite, galena

silicates = quartz, feldspar, olivene

Types of Silicate Minerals:

• Silicate minerals (largest group) are made from a structure called a Silicon Tetrahedron:

1. isolated tetrahedron - show fracture

Minerals

2. chain tetrahedron - cleavage, splinter

3. sheet tetrahedron - cleave in flat sheets

4. network tetrahedron - concoidal fracture

Formation of Minerals:

1. from cooling lava/magma

2. precipitate from solution

• water saturated with dissolved minerals evaporates - minerals are left behind)

Mineral Identification

Minerals are identified on their physical and/or chemical properties:

Physical Properties:

1. Color

2. Streak

3. Luster

4. Hardness

5. Breakage (Cleavage/Fracture)

6. Density (Specific Gravity)

Physical Properties1. Color - not dependable for identifying most minerals

• most minerals can have many colors

ex. hematite - black, gray, silver, brown, red

• very few common minerals have only one color

ex. sulfur - yellow

• many minerals are the same color

ex. black - magnetite, hematite, mica, hornblende sulfur hematite

2. Streak - color of the powder when a mineral is rubbed on a streak plate

• very reliable for identification

• streak for a mineral is always the same color (no matter the color of the mineral)

ex.: hematite - reddish-brown streak

3. Luster - the way a mineral shines/reflects light

a. Metallic - shines like a metal - galena, pyrite

b. Non-metallic - does not look like a metal:

• pearly - mica

• glassy - quartz, halite

• dull/earthy - hematite (red ochre)

• waxy - talc

• brilliant - diamond

Physical Properties

4. Hardness - how easily a mineral is scratched

• use fingernail and glass plate:

– fingernail has a hardness of 2.5

– glass has a hardness of 5.5

Moh's Hardness Scale

5. Breakage

• Cleavage - mineral breaks along smooth, flat surfaces (due to internal structure of atoms)

• the atomic structure of minerals gives minerals a characteristic crystal shape

• six basic crystal structures are:

Galena, Halite Chalcopyrite Olivene Mica, Gypsum Feldspar Quartz, Calcite

• Fracture - mineral breaks unevenly, irregularly, or in jagged surfaces

Physical Properties

6. Density (Specific Gravity) - how heavy a mineral of a given volume is compared to water

• heavy - galena, gold

• medium - quartz, feldspar

• light - mica, sulfur

"heft"

Other Properties

1. Chemical - calcite will react with HCl - bubbles or "fizzes"

2. Magnetic - magnetite is naturally magnetic

3. Double Refraction - calcite

4. Radioactivity - pitchblende - contains uranium

5. Fluorescence - some minerals glow in UV light

6. Taste - halite tastes salty

7. Smell - sulfur smells like rotten eggs

Uses of Minerals

Ore - a mineral that contains metals and non-metals that can be mined in useable amounts for a profit

• metals - conduct heat and electricity

• alloys - a mixture of 2 or more metals and non-metals (ex.: bronze, brass, steel)

• Non-metals - poor conductors of heat and electricity

• Gems - hard(>7), rare, high luster and clarity

RocksRocks are composed of 1 or more minerals:

• Monomineralic - made from just one mineral

• Polymineralic - made from 2 or more minerals

• There are only a few common rock-forming minerals:

• quartz

• potassium feldspar

• plagioclase feldspar

• pyroxene

• amphibole

• mica

• olivine ex.: granite

Rocks are classified on the basis of their formation (origin)

• Three Classes of Rocks:

1. Igneous - from molten magma or lava

2. Sedimentary - from sediments

3. Metamorphic - from heat/pressure/chemicals changing the minerals in a pre-existing rock

Igneous RocksIgneous Rocks - form from the cooling and solidification (crystallization) of

molten lava and magma

Types of Igneous Rocks are based on:

1. Environment of Formation

• Extrusive

• Intrusive

2. Mineral Composition

• felsic

• mafic

Reference Tables p.6

Igneous Rocks

1. Extrusive Igneous Rocks (Volcanic) -form from the fast cooling of lava at/near Earth's surface

• small/no crystals

• fine/smooth texture

Environment of Formation:

2. Intrusive Igneous Rocks (Plutonic) - forms

from the slow cooling of magma deep

within the Earth

• large, visible crystals ("salt and pepper" look)

• coarse, rough texture

Igneous Rocks

rate of cooling

crystal size

Note: time and rate are opposites - as time of

cooling increases, cooling rate increases

As the rate of cooling increases, crystal size decreases

• Mineral Composition - felsic or mafic

1. Felsic - rich in aluminum

• light in color

• low in density

2. Mafic - rich in magnesium and iron

• dark in color

• high in density

All igneous rocks have a few, common characteristics which make them easy to identify:

1. scattered inter-grown crystals - gives some igneous rocks a "salt and pepper" look

2. glassy texture

3. vesicular (contains air/gas pockets)

Igneous Rocks-Tree Diagram

granite

Felsic

(Al)

gabbro

Mafic

(Mg, Fe)

Intrusive

cools slowly inside earth

pumice

obsidian

rhyolite

Felsic

(Al)

scoria

basalt

Mafic

(Mg, Fe)

Extrusive

cools quickly nearor at surface

Igneous Rocks

crystallized from molten minerals

Environment

of Formation

Mineral

Composition

Examples of each class of rock

Texture

Scattered

Intergrown

Crystals

Glassy,Vesicular,

Fine Grained Identifying

Characteristics

Classifying

Characteristics

Cooled Slowly Cooled Quickly

Sedimentary RocksSedimentary Rocks - form in horizontal layers from the accumulation of sediments, organic matter, or chemical precipitates

Types of Sedimentary Rocks:

1. Clastic

2. Crystalline

3. Bioclastic

Reference Tables p.7

• process is called lithification

1. Clastic- form from physically weathered particles that are compressed and cemented together

• classified by particle size

• particles often visible

• have a "dirt" look to them

2. Crystalline - form from chemically weathered (dissolved) minerals that precipitate out when water evaporates or changes temperature

• classified by composition

• evidence of former evaporating seas

• very fine grained, soft crystallized precipitates

3. Bioclastic (Organic) - form from the accumulation of plant/animal matter

• formation of coal:

Sedimentary RocksCharacteristics for identification:

• composed of visible fragments/particles that have been cemented together

• layered appearance - throughout sample

• contains fossils

• make up about 5% of the Earth's Crust

• make up about 80% of the rocks at the Earth's surface

Sedimentary Rocks - Tree Diagram

Shale

Siltstone

Sandstone

Breccia

Conglomerate

Clastic

physicallyweathered

Rock Salt

Rock Gypsum

Limestone

Crystallinechemically

weatheredprecipitates

Bituminous Coal

Coquina

Fossiliferous Limestone

Biological

organicsediments

Sedimentary from

cemented sediments

Classified

by Size of

Particles

Classified by

Composition

Classified by

Composition

cemented fragments

soft,tiny crystals fossils

LAYERING

Metamorphic RocksMetamorphic Rocks - form from other preexisting rock (igneous, metamorphic, sedimentary) that have been changed by:

1. Heat

2. Pressure

3. Chemical Activity

• these conditions are associated with the deep burial and pressure that result from mountain building

Reference Tables p.7

Note: no melting involved!!

Recrystallization - the growth of new mineral crystals without melting

• occurs under conditions of high temperatures and/or pressures

Metamorphic Rocks

Changes in a Rock due to Metamorphism:

1. increased density - rock is squeezed under pressure

2. new minerals - due to recrystallization

3. banding - layered arrangement of intergrown crystals - due to directional pressure

4. flattened minerals - due to directional pressure

5. distorted structure - curving/folding of layers due to pressures exerted from different directions

Types of Metamorphic Rocks:

1. Foliated - mineral crystals arranged in bands

2. Non-foliated - no banding

gneiss

schist

phyllite

slate

Foliatedshow mineral

alignment/banding

hornfels quartzite marble metaconglomerate

NonFoliated

Metamorphic Rocksrecrystallized from

heat and/or pressure

Classified by

Degree of

Metamorphism

and Grain Size

Classified by Composition

Metamorphic Rocks - Tree Diagram

Rock Cycle

Rock Cycle - any class of rock can change and form into another class of rock

• Sedimentary Rocks form from the

compaction/cementation of sediments

• Igneous Rocks form the solidification of molten rock

• Metamorphic Rocks form from re-crystallization due to

heat/pressure

Reference Tables p.6