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• Solid• Inorganic• Definable chemical

composition• Orderly arrangement

of atoms in a lattice

What is a crystal?

Single, continuous piece of crystalline material bounded by flat surfaces

Flat surfaces = crystal faces

quartz

Crystals have an orderly arrangement of atoms or ions

• The shape of the crystal reflects the internal atomic structure.

Properties used to identify minerals

• Luster• Color• Streak • Hardness• Specific Gravity• Crystal Form• Cleavage• Special Properties

Streak

• Color of the powdered form

• Use a ‘streak plate’

Varieties of Hematite streak a reddish-brown

Cleavage vs. Crystal face

• Cleavage planes repeat• No repetition of crystal

face within crystal

CleavagePlanes

CrystalFaces

Cleavage

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

Cleavage example in Calcite

Cleavage planes look like box that has

been pushed over

Planes of cleavage are

parallel to each other

Cubic cleavageTwo directions

at 90

Cleavagein Halite

(salt)

Notice how this sample shows many crystals

grown together

Cleavage planes

Moh’s Hardness ScaleHardness 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

-- nail 5) Apatite

-- window glass or typical knife blade at under 5.5 6) Orthoclase

-- streak plate or good steel file at over 6.5 7) Quartz 8) Topaz 9) Corundum 10) Diamond

Soft

Hard

LusterDescribes how a mineral

reflects light– metallic– nonmetallic

• earthy• greasy• vitreous

Color• Often not reliable!– May result from impurities

• Except for some…– Olivine = olive green

Sulfur = yellow