Chapter 2 Section 2Minerals

What is a mineral? What are the components of a mineral?

1. Naturally occurring2. Solid substance3. Inorganic 4. Orderly crystalline structure5. Definite chemical composition Ex: Quartz SiO2 (silicon & oxygen)

ALL rocks are COMPOSED of minerals

1. Naturally Occurring

Minerals are formed by natural, geologic processes

Must naturally occur in nature, cannot be man-made• i.e. synthetic gems are not

considered minerals.

2 & 3. Inorganic Solid Substance

Minerals are a solid…. not a liquid…not a gas.

• within temperature ranges that are normal for Earth.

Inorganic crystalline solids found in nature• Table salt is a mineral

inorganic• Sugar is not mineral organic• Exception: many marine animals

secrete inorganic compounds calcium carbonate minerals

(coral reefs and in shells)

4. Crystalline Structure

Atoms are arranged in an orderly, repetitive structure (crystal lattice) Ex: gemstone opal isn’t a mineral has the same elements

as quartz (mineral) but NO orderly internal structure

5. Chemical Composition

A mineral has a chemical composition defined by a chemical formula Compounds made of 2+ elements

Exceptions: gold & silver 1 element (native form)

Pyrite“Fool

s Gold”FeS2

Au

How Minerals Form 4 major processes by which

minerals form:1. Crystallization from magma2. Precipitation3. Changes in pressure and

temperature4. Formation from hydrothermal

solutions

Crystallization from Magma

• Magma = molten rock• Magma cools

elements combine to form minerals• Ex: quartz &

feldspar• First to crystallize

ones rich in iron, calcium, and magnesium• Each mineral begins to

crystallize at a different temperature

Precipitation All water in Earth’s lakes, rivers,

oceans etc. contain dissolved substances• Water evaporates dissolved substances

react to form minerals• Change in water temperature dissolved

material precipitates out• Supersaturated• Ex: limestone caves, Great Salt Lake, Utah

Mono Lake, CA limestone towers (calcite) formed

underwater from calcium rich springs exposed as

sea level drops

Pressure & Temperature Existing minerals

subjected to changes in pressure and temperature• Increase pressure

Minerals recrystallize while still solid

Atoms rearranged forms compacted minerals

• Change in temperature Minerals may become unstable Form new minerals stable @

new temperature

Hydrothermal Solutions Very hot mixture of water &

dissolved substances• Have temps. between 100°C and

300°C• Solutions come in contact w/

existing minerals chemical reactions occur new minerals

• Solutions cool elements combine

• Supersaturated Ex: Bornite and chalcopyrite (sulfur

minerals) formed from thermal solutions

Mineral Groups Common minerals, together with the

thousands of others that form on Earth, can be classified into groups based on their composition.• Silicates• Carbonates• Oxides• Sulfates and sulfides• Halides• Native elements

Okenite - a silicateFluorite - a halide

Galena - a sulfide

Silicate Structure Most common group Silicon and oxygen combine to

form a silicon-oxygen tetrahedron• Tetrahedron consists of 1 silicon

atom & 4 oxygen atoms silicate Silicon-oxygen tetrahedra can

form chains, sheets, & 3-D networks• Super strong bonds• Ex: olivine-millions of single

tetrahedra (Fe,Mg)2SiO4) iron-magnesium silicate

Silicate Formation Most silicate minerals crystallize from

magma as it cools• Can occur at or near surface of Earth (temp. and

pressure low) Weathering & mountain building form silicates

• Can occur at great depths (temp. and pressure high)

Location during formation & chemical composition of magma determines which silicate minerals will form• Olivine: 1200°C Quartz: 700°C

Carbonates 2nd most common mineral

group Contain the elements:

• carbon• oxygen• one or more other metallic

elements Calcite (CaCO3): most

common carbonate mineral Limestone & marble rocks

that are composed of carbonate minerals

Oxides Contains:

• Oxygen• One or more other elements (usually

metals) Ex: Rutile (TiO2)

• Form as magma cools beneath Earth’s surface

• Titanium oxide Ex: Corundum (Al2o3)

• Existing minerals heat & pressure• Aluminum oxide

Sulfates and Sulfides Contain the element sulfur Sulfates =

• Ex: Anhydrite (CaSO4)• Ex: Gypsum (CaSO4 2H2O)

Forms when mineral-rich water evaporates Sulfides =

• Ex: Galena (PbS)• Ex: Pyrite (FeS2)• Forms from thermal solutions

Halides Contains:

• Halogen ion• One or more other elements

Halogens from Group 7A in periodic table• Includes fluorine and chlorine

Halite (NaCl) i.e. table salt Fluorite (CaF2) used in making steel

• Forms when salt water evaporates

Native Elements Minerals in relatively pure form Ex: Gold (Au), Silver (Ag), Copper

(Cu), Sulfur (S), Carbon (C)• Native forms of carbon are diamond and

graphite• Some form from hydrothermal solutions