Gemology

thumb|Main emerald producing countries

thumb|upright=1.1|Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic [[sapphire, ruby, uncut emerald, and amethyst crystal cluster.]]

Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium, and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. Corundum has two primary gem varieties: ruby and sapphire. Rubies are red due to the presence of chromium, and sapphires exhibit a range of colors depending on what transition metal is present. A rare type of sapphire, padparadscha sapphire, is pink-orange.

ratio of the speed of light in vacuum to that in the medium

right|thumb|A calcite crystal laid upon a graph paper with blue lines showing the double refraction right|thumb|In this example, optic axis along the surface is shown perpendicular to plane of incidence. Incoming light in the polarization (which means perpendicular to plane of incidence – and so in this example becomes "parallel polarisation" to optic axis, thus is called extraordinary ray) sees a greater refractive index than light in the polarization (which becomes ordinary ray because "perpendicular polarisation" to optic axis) and so polarization ray is undergoing greater refraction on ent

thumb|upright=1.25|Examining a pink sapphire under a gemmological microscope Gemology or gemmology is the science dealing with natural and artificial gemstone materials. It is a specific interdisciplinary branch of mineralogy. Some jewelers (and many non-jewelers) are academically trained gemologists and are qualified to identify and evaluate gems.

ability of a solid material to exist in more than one form or crystal structure

thumb|Pleochroism of cordierite shown by rotating a polarizing filter on the lens of the camera thumb|Pleochroism of tourmaline shown by rotating a polarizing filter on the lens of the camera

any material trapped inside a mineral during its formation

thumb|right|Tiger's eye thumb|right|Tiger's eye

star-shaped concentration of light reflected or refracted from a gemstone

thumb|A faceted amethyst Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cut into them in order to improve their appearance by allowing them to reflect light. The earliest diamond cutting techniques were simply to polish the natural shape of rough diamonds, often octahedral crystals. It wasn't until the 14th century that faceting, the process of cutting and polishing a gemstone to create multiple flat

research institute in Carlsbad, California

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manufacturing process of synthetic gemstones

medieval treatise on the properties of stones

A dichroscope is a pocket instrument used in the field of gemology, and can be used to test transparent gemstones (crystals). Experienced gemologists, observing the pleochroism of some gems, can successfully detect gemstones from other artificial stones using this instrument.

relating to the appearance of internal and surface defects in diamond

color due to impurities or crystal lattice defects in diamond

types of Gemstone found in Pakistan

Glyptology is the study of engraved gems, or of engravings on gems.