Post on 23-Feb-2016
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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