Minerals

Mineral - A naturally occurring inorganic solid with specific chemical composition and a definite crystalline structure.

• Materials made in a lab are not minerals.• Materials that are alive or were once alive

are not minerals.• No gas or liquid can be considered a

mineral.• A mineral is a crystal which is arranged in

repeating geometric pattern.

Formation of Minerals(two ways)

1. Minerals are formed from the cooling of magma.

• As magma is forced up to the crust it cools and the atoms begin to interact chemically.

• The rate of cooling determines the size of the mineral.

• The slower the cooling the larger the crystal

2.Minerals Formed From Solution

• Minerals can form from a solution that has become saturated.

• When they reach saturation (supersaturated) they precipitate.

• Secondly, when minerals dissolve in a solution and then the liquid evaporates. Ex. Gypsum and halite

Silicate - tetrahedron

Mineral Shapes

Mineral Groups

• 1. Silicates- Makes up 96% of the minerals found in the Earths crust. Are composed of oxygen and silicon and one or more elements.

• S and O bind in a tetrahedron shape (see fig. page 81)

• Examples of silicates are Feldspar, quartz, and Mica

Feldspar

Mica ex of cleavage

Carbonates• Carbonates- Are minerals composed of one

or more metals and a carbonate (CO3 ).

• Examples , calcite, dolomite, & rhodochrosite, malachite and azurite see p. 83.

Carbonates are found in rocks such as marble and limestone.

carbonates

malachite azurite

Coquina

Limestone

Marble

Oxides• Oxides- Are composed of oxygen and a

metal.• Examples are Hematite (Fe2O3) and

magnetite(Fe3O4)• Uranitite contains uranium which is used to

generate nuclear power.

Final note: Minerals formed in a open space look different from minerals that formed in a closed space, see p. 79

Hemitite

Uraninite• Major source of

uranium used to generate nuclear energy

Magnetite Fe3O4

• Hematite and magnitite are good sources of iron

Other major mineral groups

• Sulfides-pyrite• Sulfates-anhydrite• Halides-halite• Native elements-copper

metal

copper

Mineral Identification

1. Color – The presence of trace or compounds within a mineral.

Ex. Red Jasper Quartz has traces of iron oxides.

Ex. Milky cloudy Quartz could be bubbles of gas or liquid trapped in the mineral.

2. Luster

The way a mineral reflects light.Luster can be described as metallic or

non-metallic.EX. Silver, gold, copper, and galena are

metallic. Other luster descriptions are: Dull,

pearly, waxy, or silky.

3. Texture- Is how a mineral feels to the touch.

Descriptive words used: Smooth, rough, ragged, greasy, soapy, or glassy.

4. Streak Certain minerals leave a streak of color when

run across an unglazed porcelain tile. The streak is not always the same color as the mineral.

Ex. Pyrite is a gold color but leaves a greenish black streak.

No matter how much a mineral is weathered or which color it is the streak is always the same.

Streak can only be used on minerals softer than porcelain.

5. Hardness• Measure how easily a mineral can be

scratched.• Fredrick Moh developed a scale in

which the hardness of a mineral can be compared to the hardness of ten known minerals this is known as Moh’s Scale. See on page 86 Table 4-3.

Moh’s Scale

6. Fracture and cleavage• Atomic arrangement determines how

minerals will break. Minerals break along planes where atomic bonding is weak.

• Ex. Mica is said to have cleavage because it breaks in flat planes.

• Ex. Obsidian breaks with a rough or jagged edge and is said to fracture.

fracture cleavage

7. DensityDensity • Is the atomic mass• Is expressed as ratio of mass divided

by its volume. D=m/V• Geologist use Specific Gravity to

measure Density which is the ratio of weight of a substance to an equal amount of water.

Special Properties• Island spar a type of calcite, causes light to

bend as it passes through the mineral. As you look through it , you will see double images.

• This is known as double refraction, zircon exhibits this special property as well.

• Calcite (CaCO3) also fizzes when it comes in contact with Hydrochloric acid (HCL).

CaCO3 + 2HCL CaCl2 + H2O + CO2

Other special properties…..

• Magnetism ex. Magnetite• Distinctive rotten-egg odor when

streaked on a plate ex. Sphalerite as a result of the

presence of sulfide in the mineral.

Ore

A mineral is an ore if it contains a useful substance that can be mined for a profit.

• Ex. gold, silver, titanium, & aluminum

Gem • Valuable minerals

that are prized for their beauty and rarity.

Ex. ruby, emerald (more valuable than diamonds), diamond, satfire.

Trace elements

• Found in some gems. • Ex. Amethyst contains trace element

which give the gem a lovely purple color.

• Sapphires contain trace amounts of cobalt or titanium.

Mineral Uses

• Computers• Cars

Televisions• Desks• Roads • Medicines

• Building• Jewelry• Beds• Paints• Sports

equipment