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21 Cards in this Set
- Front
- Back
Crystal |
Any solid with an ordered structure, regardless of whether or not this is evident in its external form |
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Crystalline |
Internal arrangement of atoms in a solid that is very ordered |
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Unit Cell |
Smallest unit of this structure which possesses same symmetry and properties as entire mineral |
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Crystal systems |
Isometric Tetragonal Hexagonal Orthorhombic Monoclinic Triclinic
Acronym: Ingrid Takes Heroin Or Meth Too |
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Isomorphs |
Minerals with similar crystal structure and slightly different chemical compositions |
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Polymorphs |
Minerals with same chemical composition and different structure i.e. graphite and diamond |
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Miller Indices |
3-4 digits written inside brackets to represent intersection of a crystal face with x,y,z axes
(x y z)
(x y z w) |
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Crystal defects |
Point: absence of an atom or ion in the lattice
Line: dislocations |
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Solid solution |
Introduction of atoms/ions into homogeneous structure |
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Exsolution |
Initially homogeneous solid solution separates into two distinct parts without splitting |
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Crystal twinning |
Two separate crystals share some of the same crystal lattice points in a structure |
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Visible light/white light |
Electromagnetic radiation with wavelengths between 390 nm and 770 nm (purple and red) |
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Refraction |
n (index of refraction) = V_a (velocity of light in air) / V_m (velocity of light in material) |
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Isotropic minerals |
Velocity of light doesn't change inside these minerals
Isometric or amorphous |
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Anisotropic minerals |
Velocity of light changes inside minerals
Hexagonal, tetragonal, orthorhombic, monoclinic, and triclinic |
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Plane-polarized light |
White light passes through polarizing filter (Polaroid); light becomes plane-polarized: oscillations are constrained to one direction (at right angles to the beam) |
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Pleochroism |
Mineral appears to be different colours when observed at different angles |
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Relief |
Caused by difference in refractive indices of the mineral and medium
Mineral refractive index is higher than medium's then high relief is observed |
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Becke Lines |
Bright lines at the boundaries of minerals with different refractive indices |
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Extinction angle |
Angle between cleavage direction and the position where the mineral is "extinguished"
Measured from 0-89 degrees. 90 = parallel extinction (considered zero degrees) |
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Birefringence |
Light waves emerging from anisotropic mineral have different phases and interfere, showing interference colours. These can be cross-referenced with a chart to determine birefringence |