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 Si0 4 Tetrahedron shape

Identifying Minerals Over 200 known Can be identified from physical properties How 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 TERMDESCRIPTION adamantinevery brilliant - as in diamond resinous looks like resin or hardened tree sap vitreous glassy, but not as shiny as diamond metalliclooks like metal silkyhas a smooth and fibrous sheen pearlysmooth and iridescent greasylooks like it's coated with oil earthylooks 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 Magnetism Magnetite

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

Formed by cooling & hardening of magma Plutonic – intrusive, forms underground Volcanic – extrusive, forms on surface 2 kinds of magma – high SiO 2 %, light colored, thick, slow moving –low SiO 2 %, 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

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 SiO 2, CaCO 3, or FeO The Law of Superposition

Sedimentary Rock Some contain fossils

Almost all show strata (layers) Sedimentary Rock

Some show ripple marks or mud cracks

Metamorphic Rock “changed” by heat & pressure –From mountain building –Contact with magma

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