1.Gem: Strictly, gem is the natural nonmetallic mineral monocrystal. It is extremely hard and resistible to scratching (hardness up to 6 Moh’s), with bright pure color and strong luster, very transparent, and suit for the craft request. Here the gem we are talking about is the substitute of natural gem and not really the natural gem, such as cubic zirconia, synthetic ruby, synthetic sapphire, synthetic spinel, glass and so on artifical product.
2.Gem’s color: Gem is the precious treasure with beautiful color in the nature.Some gem is pure bright, and some is florid.Its color is a very important element, and a little change in color can badly affect its value.So gem’s color must be bright like the sun, pure as a lily, and brilliant like the flash, that tree features are complements to each other, not a single one can be omitted.Synthetic gem has many color, such as white, black, light golden, dark golden, pawpaw yellow, red, pink, tangerine, pomegranate red, mauve, green, olive, apple green, blue, water blue, change blue, violet, sapphire and so on.
3.Gem’s transparency: Transparency is the degree to which light passes through a substance. It’s one of the most important standards to value gem’s quality. The dark gem is not so transparent as the light or pure one.
4.Gem’s luster: When the light project to the surface of gemstone, some of them was refracted and assorted, and the other was reflected. The light reflected forms the gem’s luster. Various gems have various texture, hardness, and the reflectivity and absorptionto light differs from each other, so their luster is different. That’s why the diamond’s luster is very bright and amazing when the emerald’s luster is soft. Luster is also is one of the important standards to value gem.
5.Gem’s density: Density is the mass per unit volume of gem. Its unit is gram/cm3.The table below shows the densities of common gems: