Minerals, Rocks and the Rock Cycle

What is a mineral?

• Occurs naturally• Is a solid• Definite chemical

composition• Atoms arranged in

orderly pattern

May Be Elements or Compounds

• Native Minerals– Form uncombined in

nature– Au, Ag, Cu, S, C – Gold, silver, copper,

sulfur, diamond

• Most are compounds– Form from magma– Form as evaporites– Changed by heat,

pressure, or water

Silicates

• 90% minerals on Earth– Most common

• Si, O, and 1 or more metallic ions

• Si04

• Tetrahedron shape

Identifying Minerals

• Over 200 known• Can be identified from

physical propertiesHow can I tell what this is?

Identification Properties

• COLOR– Least useful

– Many have similar colors

– Other elements may change color

– Beryl (emerald)

Colors of Quartz

Identification Properties• LUSTER

– The shine in reflected light

LUSTER TERM DESCRIPTION

adamantine very brilliant - as in diamond

resinouslooks like resin or hardened

tree sap

vitreousglassy, but not as shiny as

diamond

metallic looks like metal

silky has a smooth and fibrous sheen

pearly smooth and iridescent

greasy looks like it's coated with oil

earthy looks like dirt

LUSTER

• Glassy• • Adamantine• • Greasy

Identification Properties

• CRYSTAL SHAPE– Hard to find– Must have room to

grow– Crystal Systems

• Cubic• Orthorhombic• Tetragonal• Triclinic• Hexagonal• Monoclinic

CRYSTAL SHAPE

Identification Properties

• STREAK– Color of its powder

– Does not change

– Metallic: as dark as sample

– Nonmetallic: white to colorless

Streak Plate ↑

Identification Properties

• CLEAVAGE– Tendency to split

easily or break along flat surfaces

– Mica – 1 direction

• FRACTURE– Break on uneven

surfaces

– Conchoidal - obsidian

Identification Properties

• HARDNESS– Resistance to being

scratched

– Mohs’ Scale of Hardness

Mohs’ Scale of Hardness

• 1 - Talc – fingernail scratches it easily

• 2 - Gypsum – fingernail scratches it

• 3 - Calcite – copper penny just scratches it

• 4 - Fluorite – steel knife scratches it easily

• 5 – Apatite – steel knife scratches it

• 6 – Feldspar – steel knife does not scratch it easily; it scratches window glass

Mohs’ Scale of Hardness

• 7 – Quartz – hardest common mineral; it scratches steel and hard glass easily

• 8 – Topaz – harder than any common mineral

• 9 – Corundum – it scratches topaz

• 10 – Diamond – hardest of all minerals

Special Identification Properties

• Fluorescence

Special Identification Properties

• MagnetismMagnetite

Special Identification Properties

• Taste• This will quickly identify the mineral halite (salt). If you

are new to this process you must use this one with caution, as you never know what the unknown may be.

• Often, you may need to resort to this method (until you more fully understand other identifying traits) to differentiate halite from calcite.

• If you do taste the sample (especially in a class environment) you should realize that it has been handled by and probably tasted by hundreds of others.

Rocks & the Rock Cycle

• James Hutton – uniformitarianism

• “The present is the key to the past”

• Geologic processes that happen today happened in the past

• Earth’s present physical features were formed by these processes

Rocks & the Rock Cycle

Igneous Rocks

Igneous Rocks

• Formed by cooling & hardening of magma

• Plutonic – intrusive, forms underground

• Volcanic – extrusive, forms on surface

• 2 kinds of magma– high SiO2%, light

colored, thick, slow moving

– low SiO2%, dark colored

• called mafic

Igneous Rocks

• Grain size and texture depends on how quick cooled – Slow = large crystals

– Fast = small crystals

Igneous Rocks

• Grouped based on mineral composition – Light = granite

– Dark = gabbro

Sedimentary Rock

Sedimentary Rock

Sedimentary Rock

Sedimentary Rock • Form from sediments

hardening into rock • From pieces of other rocks clastic, sandstone, shale

• Precipitating out of a solution chemical, limestone, rock salt

• From remains of plants & animals organic, coal, limestone

Conglomerate

Sandstone

Limestone

Shale

Sedimentary Rock

• Most formed under water, but also in deserts/dunes

• Cemented together by SiO2, CaCO3, or FeO

The Law of Superposition

Sedimentary Rock • Some contain fossils

Almost all show strata (layers)

Sedimentary Rock

Sedimentary Rock

Sedimentary Rock Some show ripple marks or mud cracks

Metamorphic Rock

• “changed” by heat & pressure – From mountain

building

– Contact with magma

Metamorphic Rock

Metamorphic Rock

Metamorphic Rock

• Shale slate schist (if more H&P are added) • Shale or granite gneiss• Limestone marble

Metamorphic Rock

Shale to Slate Metamorphism

Metamorphic Rock

Marble