How are Gemstones Formed?

How are Gemstones Formed?

Gemstones which have a mineral origin, come from rocks or in gem gravels which are formed from these rocks. Rocks themselves are made up of one or more minerals which can be divided into three different categories, igneous sedimentary and metamorphic. These three rock categories are in fact each a stage in a continuous process of rock formation.


rock formation cycle


Igneous Rocks – Created by solidifying of molten rock above or below the ground. This erodes and is then deposited as sediments. The slower a hot molten rock cools and solidifies, the larger the crystals may become.

Sedimentary Rocks - Form from the accumulation and compression of eroded rock fragments from weathering (sand or mud). These may then eventually become buried back under the surface. Most Australian opal occurs in sedimentary rocks.

Metamorphic Rocks - Can be either igneous rocks or sedimentary rocks which have been changed by heat and or pressure to form new rocks with new minerals. As a result of this gemstones can be formed within them. For example, Garnets are formed in rocks called mica schusts which begin as clay and mudstones. Limestone which is then formed to marble can also contain rubies due to intense pressure and heat.

Limestone to Ruby Gemstone

( Rubies in a matrix of white marble formed by pressure and heat in rich limestone clay.) 

Minerals which are considered to be of gemstone quality may be accessible at the ground surface, be buried deep beneath earth surface or separated from rocks by erosion and carried out by rivers to the sea.

Organic Gems

Organic gems are sourced from animals and plants. Natural pearls are created around foreign bodies that have entered into shells of marine and freshwater shellfish. Cultured pearls are artificially produced by injecting foreign bodies into shellfish through human intervention on large fisheries. Amber is fossilised tree resin, collected from soft sediments or the sea.

insect in amber

(Amber is formed from the resin of trees which has fossilised over thousands of years. Sometimes insects which have been trapped the amber when it was sticky are preserved within it.) 

Where are Gemstones Found?

USA – Tourmaline, Sapphire, Peridot
Mexico – Opal
Colombia – Emerald
Brazil – Emerald, Topaz, Garnet, Opal, Aquamarine, Chrysoberyl, Tourmaline, Diamond
Germany – Topaz
Italy – Tourmaline
Russia – Topaz, Garnet, Aquamarine, Chrysoberyl, Diamond
Egypt – Peridot
Nigeria – Topaz
Zaire- Diamond
Zambia – Emerald
Botswana – Diamond
South Africa – Diamond
East Africa – Ruby, Tourmaline, Garnet
Madagascar – Aquamarine, Tourmaline
Sri Lanka – Sapphire, Topaz, Chrysoberyl
India – Garnet, Chrysoberyl
Pakistan- Emerald
Afghanistan – Ruby, Aquamarine
Burma Ruby, Peridot
Thailand- Ruby, Sapphire
Chine Peridot, Pearl
Japan – Pearl
Australia- Pearl, Opal, Sapphire, Diamond