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 absorption to 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:

English

 

 

 

 
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Gems name
Density(gram/cm3)
Diamond
3.52
Synthetic ruby, sapphire
3.99
Cubic zirconia
5.80
Synthetic spinel
3.60
Topaz
3.533.56
Crystal
2.66
Glass
2.22

6.Gem's hardness: Gem's hardness means its resistance to scratching and whet. We always use Moh's to show it's hardness. The table below shows its class:

 

 

Moh's
1
2
3
4
5
6
7
8
9
10
The normal mineral
Steatite
Plaster
Calcite
Fluorite
Apatite
Feldspar
Quartz
Topaz
Corundum
Diamond

The hardness of common gems:

Gems name
Diamond
Synthetic ruby, sapphire
Cubic zirconia
Synthetic spinel
Topaz
Crystal
Glass
Hardness
10
9
8.5
8
8
7
5.5

The hardness of common comparative object:

Hardness
2.5
3
5.5
67
9.5
Common comparative object
Nail
Copper coin
KnifeGlass
Steel file
Carborundum

7.Gem's refractive index: The media's refractive index is the ratio of light's velocity through air (299550km/s) to the light's velocity through the media. The higher the refractive index is, the smaller the reflect angle is, and the more liable all the light is reflected, so the stronger the substance's luster is.

The refractive index of common gems:

Gems name
Diamond
Synthetic ruby, sapphire
Cubic zirconia
Synthetic spinel
Topaz
Crystal
Glass
Refractive index
2.42
1.77
2.15
1.71
1.62
1.55
1.59

8.Gem's dispersion: Dispersion is a gem's ability to bend white light into the color of spectrum. We always call it "fire", "sparkle". The dispersion is also called the ability of dispersion. Gem's dispersion is the margin between refractive index of violet and refractive index of red light, and shows the intensity of dispersion. The higher the dispersion degree is, the more obviously the gem disperses. When the gem 's dispersion is above 0.03, we call it high dispersion degree gem.

The dispersion of common gems:

Gems name
Diamond
Synthetic ruby, sapphire
Cubic zirconia
Synthetic spinel
Topaz
Crystal
Glass
Dispersion
0.044
0.018
0.060
0.020
0.0140
0.013
0.010
From the data above, we can know that the various data of synthetic gem, such as cubic zirconia,synthetic ruby,synthetic sapphire, is very close to natural diamond's, and its price is very low. Now, they are used in many trades like jewelry, artwork, watch and rag trade, so the gem's developing prospect is very fine.