-
Diamonds originate under extremely high pressure
-
150 km deep, in the upper mantle
-
Pure carbon is compressed into the diamond structure
-
Rifting causes deep-mantle rock to move upward
Mineral Crystals
-
Mineral crystals form when a melt solidifies
o
Quick cooling = tiny crystals
o
Slow cooling = large crystals
-
New crystals can form from an aqueous solution when dissolved.
o
Evaporation of water is a common way for this to happen
-
When rocks are buried at great depths, new crystals may form
o
Chemical reactions at high temperatures and pressures result in
the genesis of new minerals at the expense of the old through
solid-state diffusion
-
Biomineralization forms new crystals
o
Our teeth enamel is mineral apatite
-
Mineral crystals can sometimes precipitate directly from a gas
Mineral Formation
-
A tiny early crystal acts as a seed for further growth
-
Atoms migrate to the seed and attach to the outer face
-
Growth moves faces outward from the center
-
Unique shape reflects the crystal’s internal atomic order
-
Outward crystal growth fills available space
-
Resulting crystal shape is governed by surroundings
o
Open space – good crystal faces grow
o
Confined space – no crystal faces
o
Crystals develop outward from a central seeds and fills the
existing space
-
Mineral growth is often restricted by a lack of space
o
Anhedral – grown in a tight space
o
Euhedral – grown in an open cavity, good crystal faces
Mineral Destruction
Melting – heat breaks the bonds holding the atoms together
Dissolving – solvents (mostly water) break atomic bonds
Chemical reaction – reactive materials break bonds
Physical properties
1) Color
2) Streak
3) Luster
4) Hardness
5)
Specific gravity
6)
Crystal habit
7)
Fracture or cleavage
Color
The part of the visible light that is absorbed by a mineral (the color you see
is the wavelength it does not absorb)
Streak
Color of the powder residue when the mineral is crushed or scraped against
porcelain
Luster
The way the mineral surface scatters the light (metallic, non-metallic)
Hardness
Resistance to scratching (depends on the atomic bonds) MOHS SCALE.
Lowest = talc, graphite
Highest = diamond
Specific Gravity
Density of the mineral, or how heavy it “feels”. Galena “feels” heavier than
Quartz.
Crysal Habit
A single crystal with well-formed faces. Records variation in directional
growth rates.
Special properties
1.
Effervescence – reactivity with an acid
2.
Magnetism – magnetic attraction
3. Taste
4. Smell
5. Feel
6.
Elasticity – response to bending
7.
Diaphaneity – relative transparency
8.
Piezoelectricity – electric charge when squeezed
9.
Pyroelectricity – electric charge when heated
Fracture
-
Minerals break in ways that reflect atomic bonding
-
Different minerals break in different ways
-
Cleavage forms in directions where the bonds holding the atoms
together are the weakest.
