Geology! Geology! Geology! Geology!

What is Geology? Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them. It includes the study of organisms that have inhabited our planet. An important part of geology is the study of how Earth’s materials, structures, processes and organisms have changed over time.

Minerals … Why study ‘em? Building blocks of planet Industrial minerals Ore minerals Energy resources Gems Environmental hazards

What is a mineral? Homogeneous Naturally occurring Inorganic Solid Definable chemical composition Orderly arrangement of atoms in a lattice Quartz Hematite

What is a crystal? A piece of homogeneous solid substance having a natural geometrically regular form with symmetrically arranged plane faces. Quartz Halite

Crystals have an orderly arrangement of atoms or ions The shape of the crystal reflects the internal atomic structure. Halite crystals Atomic structure of Halite

Properties used to identify minerals Luster Color Streak Hardness Crystal Form Cleavage Special Properties Specific Gravity

Luster Describes how a mineral reflects light –Metallic minerals have the lustre of polished metal

Luster Describes how a mineral reflects light –Nonmetallic “Pearly” “Vitreous” (glass-like) “Dull” or “Earthy”

Luster Describes how a mineral reflects light –Nonmetallic “Silky” “Waxy” “Greasy”

Color Often not reliable!Often not reliable! –May result from impurities Except for some…Except for some… –Olivine = olive green Often not reliable!Often not reliable! –May result from impurities Except for some…Except for some… –Olivine = olive green Sulfur = yellow

StreakStreakStreakStreak Color of the mineral when in powdered form Varieties of Hematite streak reddish-brown White Streak Plate Streak color

Moh’s Hardness Scale Hardness is a measure of a minerals resistance to being scratched. It is determined using the “scratch test.” Moh’s Scale is based on a relative scale based on minerals and common materials. 1) Talc 2) Gypsum -- fingernail at 2.5 3) Calcite -- copper (old penny) at 3.5 4) Fluorite 5) Apatite -- nail 6) Feldspar -- streak plate or good steel file at over 6.5 7) Quartz 8) Topaz 9) Corundum 10) Diamond Soft Hard

Cleavage Tendency of a mineral to break on flat planes of weakness.

Cleavage vs. Crystal face Cleavage planes repeat No repetition of crystal face within crystal CleavagePlanes Crystal Faces Crystal Faces

Cleavage example in Calcite Cleavage planes look like box that has been pushed over Planes of cleavage are parallel to each other Notice the double refraction

Cubic cleavage Two directions at 90  Cleavage in Halite (salt) Notice how this sample shows many crystals grown together Cleavage planes