Minerals

What is a mineral?

• Naturally occurring• inorganic (no living thing or remains)• Solid• Definite shape ( arranged in an orderly

pattern)• definite chemical composition

Is it inorganic?

• Coal?• No, it is not a mineral- How is it made?• magnetite • Yes, a mineral• pearl• No, not a mineral- How is it made?

Does it occur naturally?

• Quartz• yes, a mineral- one of the last minerals to

form from a magma chamber.• Silver• yes, a mineral• steel• no, not a mineral- How is it made?

Solid in crystalline form?

• Petroleum• no, not a mineral- What is its natural form?• mercury• no, not a mineral- What is its natural form?• glass• not a mineral- What is its form? • amorphous

Definite chemical composition?

• Calcium• yes, Ca a mineral• Graphite• yes, C• Concrete• no, not a mineral- Why?

Rock forming minerals

• Over 3000 minerals• only 20 are common, these are rock

forming minerals• two main groups- silicates and nonsilicates

Silicates

• 96% of the crust• contain silicon (Si) and Oxygen (O)• Feldspars are the most common silicate

minerals, contain Ca, K, and Na• Examples- Orthoclase and plagioclase• Ferromagnesium- contain Fe and Mg

Nonsilicates• 4% of the crust• No silica• Six major groups• carbonates-ex. Calcite• halides- ex halite• native elements- Made of one element ex.

copper and silver• oxides- hematite and corundum• sulfates- gypsum• sulfides- galena, pyrite

Crystal Structure

• Specific geometric arrangement of atoms or ions

• Crystal = natural solid with a definite shape• Can be seen under microscope or with the

aid of x rays

Identifying Minerals• Characteristics of Minerals• Each mineral has specific properties that

provide useful clues for identifying minerals.

• Optical properties- properties will be identified by looking at the mineral.

• Tests- tools are used to run tests on the mineral.

Optical PropertiesColor

• Most easily observed• ex. Sulfur is bright yellow, azurite is deep

blue• least reliable characteristic

– quartz consists of many colors– weathering may hide true color

Luster• Light reflected from the surface of a mineral

• metallic luster- like polished metal like silver• All others are non metallic• vitreous luster- reflects like glass• pearly luster• adamantine- brilliant luster ex. Diamond or gems• other lusters include: waxy, greasy, dull, earthy

Crystal Shape• Regularly shaped particles, or pattern. • Most crystal shapes are hard to identify.• six crystal systems

– cubic ex. Halite, Pyrite– orthorhombic ex. Sulfur– tetragonal ex. Chalcopyrite– hexagonal ex. Plagioclase, Orthoclase– monoclinic ex. Micas– triclinic ex. Kyanite

Cleavage

• The tendency to split along certain flat surfaces and is related to types of bonds

• ex. Mica (general name) splits easily in one direction, it has one perfect cleavage ( splits in parallel sheets)

• Example- biotite and muscovite

Fracture• Some minerals do not break along cleavage

planes • instead they fracture or break unevenly into

curved or irregular pieces• splintery or fibrous fracture- looks like

pieces of broken wood• conchoidal- curved surfaces like the inside

of a shell

Simple TestsStreak Test

• The color of a mineral in powdered form• observed by rubbing the mineral against a

piece of unglazed ceramic tile called a streak plate

• the streak is not always the same color as the mineral

• mineral that have a hardness higher than the streak plate can not be tested

Hardness Test• The ability to resist scratching• hardness does not mean resistance to

cleavage or fracture• the hardness of an unknown mineral may be

determined by using Moh’s Hardness Scale• -this scale lists 10 minerals in order of

increasing hardness• -Softest is talc with a hardness of 1• The hardest is diamond with a hardness of

10

Moh’s Hardness Scale• Mineral hardness common test• talc 1 easily scratched by fingernail• gypsum 2 can be scratched by fingernail• calcite 3 can not scratch a copper penny• fluorite 4 can easily scratch a penny • Apatite 5 can barely scratch glass• Feldspar 6 can scratch glass • quartz 7 very easily/deeply scratches steel and glass• topaz 8 scratches quartz• corundum 9 no simple tests• diamond 10 scratches everything

Specific Gravity

• The ratio of the weight of the mineral to the weight of an equal volume of water.

• Each mineral has its own specific gravity• Can be used to identify a mineral

Acid Test

• Used to easily identify calcite

A drop of HCl dropped onto Calcite will cause it to effervesces. The bubbles are CO2 gas.

• Dolomite also responds to the acid test but not as violently and only in powdered form.

Special Properties• Magnetism- Can attach a magnet• Fluorescence- the ability to glow under

UV light ex. Calcite appears red under UV

• Phosphorescence- minerals that continue to glow after a UV light is removed.ex sphalerite

Special Properties con’t• Double refraction-

crystals that bend light in such a way that they produce a double image of any object viewed.

• Radioactivity- certain atoms have unstable electron or neutron arrangements. These minerals activate a Geiger counter.

End of Minerals