|
Sponsored Links
A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive mineral, which — when cut and polished — is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al2O3). Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example diamonds, which have a cubic crystal system, are often found as octahedrons. Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl. Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and lustre. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.
|
Gemstone Subcategories
Gemstone Articles
GEMSTONE GUIDE | RUBY EMERALD SAPPHIRE EDUCATION
by Sanjeev Prakash
Apr 07, 2008
A prior knowledge of gemstones (ruby, emerald and sapphire) will help you understand and retain what a jeweler tells you. This gemstone guide will help you in evaluating the quality of ruby, emerald and sapphire, an aid in avoiding fraud with informa...
|
|
