MINERALS AND ROCKSAN INTRODUCTION TO GEOLOGY:

MINERALOGY AND PETROLOGY

MineralsA mineral is a naturally occurring solid with a

specific chemical composition and atomic arrangement (crystalline structure).*

Quartz = Silica + Oxygen or SiO2

* Some references also add “inorganic” to the definition, but there are some rare organic minerals too (i.e., whewillite).

Methods to Identify Minerals1. Color2. Streak3. Luster4. Fluorescence5. Chemical Composition6. Hardness

1. Talc2. Gypsum3. Calcite4. Fluorite5. Apatite6. Orthoclase7. Quartz8. Topaz9. Corundum10. Diamond( Mnemonic Devise - The Geologist Can Find An Ordinary Quartz Tourists Call Diamond)

7. Specific Gravity8. Crystal Form9. Optical Properties10. Cleavage11. Fracture12. Magnetism13. Electrical Properties14. Melting Point15. Geologic Setting

Copper

Gold

Pyrite (Fool’s Gold)

Arsenic

Bauxite (aluminum ore)

Kaolin Mine Near Thomson, Georgia

Barite (rose morphology)

Quartz

ROCKS• A rock is any naturally occurring solid mass of mineral or minerals.

• There are three primary types of rocks:1) Sedimentary2) Igneous3) Metamorphic

SEDIMENTARY ROCKS

Rocks formed from accumulation and hardening of water or airborne sediment, plant or animal remains, chemical action, or evaporation.

Some of the most common sedimentary rocks are:• Limestone• Shale• Sandstone

Limestone

Limestone with fossils

Shale

Sandstone

Peat Coal

Igneous Rocks

• Igneous rocks are formed by the cooling of magma from deep within the earth

• There are two main categories of igneous rocks:

1) Intrusive – formed underground

2) Extrusive – formed above ground

The most common intrusive igneous rock is granite.

Some common extrusive igneous rocks include:

• Basalt• Obsidian• Pumice

Granite with thin-section

← Obsidian

Pumice →

Basalt – vesicular (with holes), dense, and thin-section

Metamorphic Rocks

These rocks are formed by other rocks being buried deep within the earth and subjected to very high temperature and pressure.

Common metamorphic rocks include:• Marble• Greenstone• Slate• Schist• Gneiss

Marble with thin section

Greenstone

↑Slate (plain)

Slate with Pyrite ↓

Gneiss

Schist – highly folded