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 Gold at Fort Knox 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 Flash: Minerals, Gems and Ores 24.16

Silicates 90% minerals on Earth Si, O, and 1 or more metallic ions Most common Si, O, and 1 or more metallic ions Si04 Tetrahedron shape

How can I tell what this is? 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 TERM DESCRIPTION adamantine very brilliant - as in diamond resinous looks like resin or hardened tree sap vitreous glassy, 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

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 Flash: Rock Cycle 19:41

Igneous Rocks 2 kinds of magma 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

Enormous mass of intrusive igneous rock (rock made of once-molten material that has solidified below the earth's surface). Granite, have steep walls, no visible floors, and extend over thousands of square miles. Form either as one large mass or many smaller masses at great depths and are exposed only after considerable erosion. Associated with plate boundaries.

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 Conglomerate is a sedimentary rock that contains large (greater than two millimeters in diameter) rounded clasts (pieces of rock). The space between the clasts is generally filled with smaller particles and/or a chemical cement that binds the rock together.

Sandstone

Limestone

Shale

The Law of Superposition 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

Sedimentary Rock Almost all show strata (layers)

Sedimentary Rock

Some show ripple marks or mud cracks 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

Shale to Slate Metamorphism Metamorphic Rock Shale to Slate Metamorphism

Metamorphic Rock

Marble

Poster Project: Draw and color the Rock Cycle on a large Poster board. Cut out pictures of the different kinds of rock shown and paste them to the drawing in the appropriate places. Due in 1 week.