Gemstones:

This term is restricted to those materials most suitable for personal adornment. 

Ornamental Stones - This is a complementary terminology to  Gemstones, however,” An  Ornamental stone, is stone used for decoration, they differ  from gemstones, in that they are not only used for jewelry, However, an ornamental stone may also be a gemstone. Alabaster is an example of an ornamental stone. It is used for the rails of staircases and halls in fancy buildings. Marble is an ornamental stone used for sculpture and as a building material.”

The terms, Precious and Semi precious stones have been used to distinguish different gem materials on the basis of recognized 

Value: DIAMOND, EMERALD, RUBY, SAPPHIRE Consistently 

Have been regarded as precious stones, and in cut form, they are regarded as Noble gems.

OPAL PEARL TURQUOISE and CHRYSOBERYL have been regarded as precious stones at different times. 

SPECIFICATIONS OF GEMSTONES 

The most important specification for gem materials are; 

1.    Beauty:  expressed as splendor, purity, attractive is a matter of individual appreciation.Quality of color, transparency, indices of reflection, refraction, dispersion, Freedom from imperfection in transparent variety is important. 

2.   Durability: resistance to abrasion, pitting, chipping and splitting determines the longevity of the finished product. Superior durability is required from gems mounted, and it is dependent upon hardness. 

3.   Rarity:  An essential qualification, and for stones, outweighs physical qualities,for example, emerald commands more respect (price) than many others, Variety of gems stones of the same color. Rarer varieties are more valuable. 

4.   Portability: Although of lesser effect in the value of gems, but it is sought after for obvious reasons. The bulkier ones are less preferred to the smaller more portable ones, that can be transported from place to place

5.   Hardness:The hardest minerals such as diamond, corundum, Chrysoberyl, spinel, topaz and most variety of beryl, garnet, tourmaline and zircon are superior to others for use in personal jewelry, they   can be cut into faceted gems, that take excellent and lasting polish. These minerals are above quartz on the Mohs hardness scale, hence are little affected by daily contact with materials that contain quartz, feldspar and other abrasive substances.

Classification of Gemstones

1. Basis of Identity of Gemstones as Elements and Compounds:

• Elements:
• Diamond: Pure carbon, crystallized in the cubic system.
• Graphite: Another form of pure carbon, but not typically considered a gemstone.
• Compounds:
• Corundum (Aluminum Oxide - Al₂O₃): Includes sapphires and rubies, where color is due to trace elements.
• Beryl (Beryllium Aluminum Silicate - Be₃Al₂(SiO₃)₆): Includes emerald and aquamarine.
• Quartz (Silicon Dioxide - SiO₂): Includes amethyst, citrine, and rose quartz.
• Topaz (Aluminum Silicate Fluoride Hydroxide - Al₂SiO₄(F,OH)₂):
• Feldspar (Group of Minerals - Potassium Aluminum Silicate, Calcium Aluminum Silicate, Sodium Aluminum Silicate): Includes moonstone and labradorite.

2. Basis of Hardness and Toughness:

• Hardness (Mohs Scale of Hardness):
• Diamond (10): The hardest known natural material.
• Corundum (9): Includes sapphires and rubies, very hard.
• Topaz (8): Hard, but can be cleaved easily.
• Quartz (7): Hard, common in many varieties.
• Feldspar (6-6.5): Moderately hard.
• Apatite (5): Moderate hardness.
• Fluorite (4): Softer.
• Calcite (3): Soft, easily scratched.
• Gypsum (2): Very soft.
• Talc (1): The softest mineral.
• Toughness:
• Diamond: Despite its hardness, diamond can be brittle and prone to cleavage.
• Corundum: Very tough and durable.
• Jade (Nephrite and Jadeite): Extremely tough, often used in carvings and tools historically.
• Quartz: Generally tough but can be brittle.
• Opal: Relatively soft and brittle, requiring care.
• Emerald: Often contains inclusions that reduce toughness, making it more brittle.

Conclusion:

Gemstones are classified both by their elemental and compound identities and their physical properties such as hardness and toughness. Diamonds are the hardest, while jade is one of the toughest. Each gemstone's unique composition and properties determine its use and value in jewelry and industrial applications.

Industrial Uses: From ancient times, Gems have been used by man for weapons (cryptocrystalline quartz) as, ax heads, utensils, etc. Garnet, quartz, are used for abrasives, hematite, lazurite, malachite, as pigments. Some are used for seals, lenses, engraving material, Diamond, corundum for, cutting edges, etc.