Gemstones, Understanding the Language

CLASS: The chemical composition and structure of the gem.

CRYSTAL SYSTEM: The basic symmetry of mineral at the atomic scale, which dictates how it grows.  Isometric, tetragonal, hexagonal, trigonal, othorhombic, monoclinic, and triclinic are the seven crystal systems.  Amorphous is the material that is disorganized at the atomic scale, natural glass.  Pearls, shells and opals are gem material that does not have an atomic scale.

COMPOSITION:  Atomic content that described by a mineral formula.

REFRACTIVE INDEX: Light slows down when it enters in a crystal.  The reflractive index measures this slowing.

BIREFRINGENCE: Difference between highest and lowest index with in a mineral with more than one refractive index value.

DISPERSION: Refractive index of a mineral is different depending on the spectrums associated wavelength.

SPECIFIC GRAVITY: Measures how much an object weights relative to the same volume of water.

HARDNESS: Resistance of a material to scatching.  Mohn Scale measures the hardness;       i.e.     1-Talc, 2-Gypsum,  3-Calcite,  4-Fluorite, 5-Apatite,  6-Orthoclase,  7-Quartz,  8-Topaz, 9-Corundom, 10-Diamond

CLEAVAGE:  Tendency of a mineral to break on flat plane.  Point of weakness between atoms.

FRACTURE:  Breaks along lines other than flat.

LUSTER:  Reflection of light.  Transparent mineralshave a luster, vitreous, resinour, silky, dull, earthy, or pearly. Opaque minerals may have metallic luster.

HABIT:  Common way a mineral grows.