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

Streak

Click 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