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-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 upwardMineral Crystals-Mineral crystals form when a melt solidifiesoQuick cooling = tiny crystalsoSlow cooling = large crystals-New crystals can form from an aqueous solution when dissolved. oEvaporation of water is a common way for this to happen-When rocks are buried at great depths, new crystals may formoChemical 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 crystalsoOur teeth enamel is mineral apatite-Mineral crystals can sometimes precipitate directly from a gasMineral 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 surroundingsoOpen space – good crystal faces growoConfined space – no crystal facesoCrystals develop outward from a central seeds and fills the existing space-Mineral growth is often restricted by a lack of spaceoAnhedral – grown in a tight spaceoEuhedral – grown in an open cavity, good crystal facesMineral DestructionMelting – heat breaks the bonds holding the atoms togetherDissolving – solvents (mostly water) break atomic bondsChemical reaction – reactive materials break bondsPhysical properties1) Color
2) Streak3) Luster4) Hardness5)Specific gravity6)Crystal habit7)Fracture or cleavageColorThe part of the visible light that is absorbed by a mineral (the color you see is the wavelength it does not absorb)StreakColor of the powder residue when the mineral is crushed or scraped against porcelainLusterThe way the mineral surface scatters the light (metallic, non-metallic)HardnessResistance to scratching (depends on the atomic bonds) MOHS SCALE. Lowest = talc, graphiteHighest = diamondSpecific GravityDensity of the mineral, or how heavy it “feels”. Galena “feels” heavier than Quartz. Crysal HabitA single crystal with well-formed faces. Records variation in directional growth rates.Special properties1.Effervescence – reactivity with an acid2.Magnetism – magnetic attraction3. Taste4. Smell5. Feel6.Elasticity – response to bending7.Diaphaneity – relative transparency8.Piezoelectricity – electric charge when squeezed9.Pyroelectricity – electric charge when heatedFracture
-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.