Colored Gemstones

Besides diamonds, colored gemstones have always been popular for jewelry. Sapphires, rubies, and emeralds used to be classified as precious gemstones whereas, all others were considered semi-precious. Precious and semi-precious gem designations are not used in the gem and jewelry industry any more since they are not accurate to describe the value, rarity or availability of a particular gem type. Gemstones are rare in nature and  are often enhanced in addition to faceting or shaping; through treating with heat, radiation, oils, or waxes to hide minor blemishes or to enhance the color. These processes are all considered standard practice in the gem business. Some types of beautiful natural gems that have not been enhanced can be worth as much as, or more per carat than a diamond of comparable quality, and often come with a certificate of authenticity from an independent gem laboratory.

In addition to natural enhanced stones, you can also find synthetic stones which are created or grown in a lab.  They are usually refereed to as “created” gems since the term synthetic has the perception of being fake.  Though chemically they are the same as natural stones, synthetic stones can be larger, with better color and fewer blemishes. They are also more affordable, while often only a trained professional can tell the difference.  Imitation gemstones, on the other hand are synthetic gems of one kind, often synthetic spinel, that are made to look like an other type of gem.

Each gemstone type is described with reference to its Mohs Hardness Rating, as a value on the Mohs Scale, after the Austrian mineralogist Friedrich Mohs. The hardness rating will indicate the gem’s scratch-resistance. A lower number is softer, and lower ranked gems will be scratched by stones with a higher hardness ranking.  Most gemstones can scratch glass since most glass types are about 5.5 on the Mohs scale.  Sapphire and ruby are corundum and have a Mohs hardness of 9 but diamond is 4 times harder.  The absolute hardness gives a better indication of the actual hardness differences.  Diamond is the only mineral that ranks 10 and no other natural mineral even comes close to the hardness of diamond.

The table below gives a good understanding of the relation of the Mohs hardness to the absolute hardness.

Mohs hardness Mineral Chemical formula Absolute hardness Image
1 Talc Mg3Si4O10(OH)2 1
2 Gypsum CaSO4·2H2O 3
3 Calcite CaCO3 9
4 Fluorite CaF2 21
5 Apatite Ca5(PO4)3(OH,Cl,F) 48
6 Orthoclase feldspar KAlSi3O8 72
7 Quartz SiO2 100
8 Topaz Al2SiO4(OH,F)2 200
9 Corundum Al2O3 400
10 Diamond C 1600