Gemmology

What Is a Gemstone?

A gemstone is a collective term for all ornamental stones that possess the following attributes:

1. Beauty
2. Rarity
3. Durability
4. Demand
5. Tradition
6. Portability

Gemstones have three basic origins:

1. Inorganic: minerals.
2. Organic: formed from living organisms.
3. Man-made: formed in a laboratory environment.

WHAT IS A MINERAL ?

A mineral can be defined as being of inorganic origin with a definite chemical composition, physical properties which are relatively constant and a crystalline structure.

In mineralogy, there are several thousand minerals listed but only about 100 have been cut as gemstones with fewer than 50 having the necessary qualities to be truly classed as "Gemstones".

WHAT IS A ROCK ?

A rock can be defined as any mineral or mixture of minerals that makes up an important part of the earth's crust.

Examples:

• Granite (Feldspar, Quartz and Mica)
• Lapis Lazuli: (Lazurite, Sodalite, Calcite and Pyrite)

There are three main groups of rocks, namely:

1. Igneous - Rock solidified from the molten magma either within the earth or at its surface.
2. Sedimentary - Formed from the fine deposits of sand, grit and clay which were eroded from ancient pre-existing rocks by the actions of wind, rain and flowing water to form alluvial deposits.
3. Metamorphic - Formed from Igneous or Sedimentary rocks which have been subjected to high pressure and temperatures beneath the earth's surface.

Gemstones can be further classified into:

1. Groups
2. Species
3. Varieties

Group	Species	Variety
Feldspar	Beryl Chrysoberyl Corundum Orthoclase Microcline Plagioclase	Emerald, Aquamarine Alexandrite, Chrysoberyl,Cat's Eye Chrysoberyl Ruby and Sapphire Moonstone Amazonite Labradorite
Garnet	Almandine Pyrope Grossular Andradite Spessartite Uvarovite	Purple/red Blood red Hessonite Demantoid Orange, yellow, flame red Emerald green
	Opal Quartz Chalcedony Tourmaline	Black Opal, White Opal, Fire Opal Amethyst, Citrine Agates, Cornelian, Onyx Indicolite, Rubellite,Green Tourmaline