Different Crystal, Crystalline, Glass, Imitation & Simulant.
Crystalline
Most solid subtances, whether formed in nature or in laboratory, have a definite orderly internal arrangement of their constituent atoms and are said to have a crystalline structure. Under favourable conditions of formation, crystalline subtances may develop as solids bounded by natural plane surface and are called crystal. Calcite crystal and quartz crystal are example of crystal. The natural plane surfaces are termed crystal faces. Crystalline aggregates of masses are composed of irregular grains or particles each of which possesses an orderly internal structure (for example marble). When solids are devoid of an orderly internal arrangement of atoms, they are called noncrystalline or amorphous. Glass and opal are amorphous subtances.
In crystalline subtances the various properties generally vary with direction, while in amorphous solids the individual properties are the same in all directions. In the study of crystal structure, based upon the internal arrangement of atom, X-ray methods are of the utmost importance. Many minerals are found as excellent crystal. Accurate and rapid determination of minerals can, in many cases, be most successfully made by recognizing the crystal form.
Diamonds Crystal Structure
Imitation
There will always be a market for imitations or cheaper gems because of the value of gemstones and their rarity,. Generally imitation gemstones are made to deceive. They are made from any material, natural or artificial, that looks similar enough to be taken for the real and more expensive gem. Imitations have been made since thousands of years, for example blue faience (glazed day) was used by the Egyptians to imitate turquoise. Romans and Indians used coloured glass to imitate gemstones including emeralds and rubies. The Victorians used a number of materials including glass (paste), plastics and resins to imitate both the natural mineral gemstones and the organic gems such as amber and shell.
Imitation gemstones merely imitate the color or look of a natural stone. They can be made out of anything. A cubic zirconia is an IMITATION diamond, for example. A blue piece of glass could be an imitation sapphire. A variety of blue synthetic forsterite is an excellent imitation for tanzanite, while chemically, it's composition is much closer to the yellowish green peridot. Another classic example is the "alexandrite" set in many jewelry pieces is actually a variety of vanadium colored synthetic sapphire.
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