Editing Gemology (section)

==General identification of gems==
[[File:Gem.pebbles.800pix.jpg|right|thumb|250px|A selection of ornamental, non-precious stones made by tumbling rough pebbles with abrasive grit in a rotating drum. The biggest pebble here is {{convert|40|mm|in}} long.]]
Gem identification is basically a process of elimination. Gemstones of similar color undergo non-destructive optical testing until there is only one possible identity.

Any single test is nearly always only indicative. For example: The [[specific gravity]] of [[ruby]] is 4.00, [[glass]] is 3.15–4.20, and [[cubic zirconia]] is 5.6–5.9&nbsp;. So one can easily tell the difference between cubic zirconia and the other two; however, there is overlap between ruby and glass.

As with all naturally occurring materials, no two gems are identical. The geological environment they are created in influences the overall process so that although the basics can be identified, the presence of chemical "impurities", and substitutions along with structural imperfections create "individuals".

===Identification by refractive index===
[[Image:Portable refractometer.JPG|thumb|Traditional handheld refractometer]]
One test to determine the gem's identity is to measure the refraction of light in the gem. Essentially, when light passes from one medium to another, it bends. Blue light bends more than red light. How much the light bends will vary depending on the gem mineral.

Every material has a [[Critical angle (optics)|critical angle]], above which point light is reflected back internally. This can be measured and thus used to determine the gem's identity. Typically this is measured using a [[refractometer]], although it is possible to measure it using a microscope.

===Identification by specific gravity===
[[Specific gravity]], also known as relative density, varies depending upon the chemical composition and crystal structure type. Heavy liquids with a known specific gravity are used to test loose gemstones.

Specific gravity is measured by comparing the weight of the gem in air with the weight of the gem suspended in water.

===Identification by spectroscopy===
This method uses a similar principle to how a [[Prism (optics)|prism]] works to separate white light into its component colors. A gemological [[Optical spectrometer|spectroscope]] is employed to analyze the selective absorption of light in the gem material. Coloring agents or chromophores show bands in the spectroscope and indicate which element is responsible for the gem's color.

=== Identification by inclusions ===
[[File:Three_Phase_in_Rock_Crystal_Quartz,_Pakistan.jpg|thumb|left|Three inclusion phases in rock crystal quartz]]
[[Inclusion (mineral)|Inclusions]] can help gemologists to determine whether or not a gemstone is natural, synthetic or treated (i.e. fracture-filled or heated).
{{clear}}

=== Identification by flaws and striations ===
[[File:Curved_Striations_in_Synthetic_Color-Change_Sapphire.jpg|thumb|left|The curvature observed in this synthetic color-change sapphire is due to a process known as the Verneuil process or, flame fusion.]]
During the [[Verneuil process]] for synthesizing gems, a fine crushed material is heated at extremely high temperatures. The powdered gem mineral is then melted (or a metallic mixture directly burned in an oxygen flame) the residue of which then drips through a furnace onto a boule. The boule where the [[corundum]] or [[spinel]] cools down and crystallizes, spins and thus causes the curved striations, which are diagnostic for a lab-created gem: Natural corundum does not show curved striations.

Likewise, natural stones, particularly [[beryl]] minerals, show small flaws – short planar cracks where the direction of the crystalline orientation in the gem abruptly changes. The natural formation of gemstones tends to layer the minerals in regular crystalline sheets, whereas many synthetically produced gems have an amorphous structure, like glass. Synthetics made by the Verneuil process either do not show flaws at all, or if any flaws are present, show curvy, undulating surfaces rather than flat ones.
{{clear}}