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Physical Geology
Chapter 5
Big Definition!
• Mineral – a natural, usually inorganic solid that shows– Characteristic chemical composition– Orderly internal structure– Recognizable physical properties
Coal Brass Obsidian Basalt Fluorite
Is it organic? No Yes Yes Yes Yes
Does it occur naturally? No Yes Yes Yes
Is it a crystalline solid? No Yes Yes
Does it have a consistent No Yeschemical composition?
Kinds of Minerals
• Silicates – has some combination of silicon (Si) and oxygen (O) and comprise 96% of the earth’s crust
• Non-silicates – no SiO compounds; 4% of the earth’s crust
Silicate Minerals
• Quartz – only Si and O
• Feldspar – most common silicate
• Ferromagnesians – iron and magnesium bearing compounds– olivine– Pyroxene– Amphibole– biotite
Non-Silicate Minerals
And Native Elements
• All minerals in Earth’s crust have a crystalline structure of some kind.
• That is its “regular orderly structure”
What is a crystal?
• A solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern
Diamond
• X-rays are used to study crystals
• X-rays pass through a crystal and strike a photographic plate producing an image of the atom/molecule arrangement
Silicate building block – the silicon/oxygen tetrahedron
Silicate MineralArrangements
• Isolated do not link to other O or Si
• Rings link by sharing O
• Single chains share O (open rings)
• Double chains are bonded single chains
• Sheets share 3 O with others; 4th with Al or Mg, which holds sheets
• Frameworks bond each tetrahedron to 4 others; and on and on…………..
Non-silicate arrangement
• Vast variety of crystalline structures
• May have tetrahedra similar to silicates but with different elements at center
• Minerals with same ion at center share properties, thus creating subgroups
How do we identify minerals?
• By physical properties such as– Color– Streak– Luster– Cleavage and fracture– Hardness– Crystal shape– density
• Or by special properties such as– Fluorescence– Phosphorescence– Chatoyancy– Asterism– Magnetism– Radioactivity– Double refraction
Color
• Many typical colors, but additions of elements can cause changes; e.g.,
• quartz vs. AmethystClick here for more information
Luster• Click here for more information
Cleavage and fracture• Click here for more information
Hardness• Click here for more information
Crystal shape• Click here for more information
Specific gravity• Click here for more information
Special properties• Click here for more information