How is a Gem Formed?
Understanding how a gem is formed can best be explained by using an apple as a model of the Earth. The core of the apple represents the core or middle of the Earth. The meaty portion, the white part of the apple represents the mantle that consists of 80% of the planet.
The thin skin of the apple represents the crust of our planet which only takes up about 1% volume or three to twenty-five miles.
Movement of the tectonic plates located in Earth’s solid portion of the mantle occurs very slowly over time, but from time to time does move faster when one suddenly experiences a ‘slip.’ How these different plates come into contact with one another are what bring about earthquakes and volcanism.
Gems, in their original mineral state form in the crust of the Earth with the exception of the diamond. The diamond forms in the mantle. Gems are mined in or on the crust of the Earth which consists of three types of rocks; metamorphic, sedimentary, and igneous.
• Metamorphic are the result of high temperature and pressure changes in the crystal structure of the sedimentary or igneous rocks. They are a result of pre-existing rocks transforming. Common rocks of this nature are the slate, marble, or gneiss.
• Sedimentary is formed with the deposition and cementation of the Earth’s surface. They are a collective process where mineral and organic particles settle in one place.
• Igneous rocks, also known as volcanic rocks form at the surface of the Earth’s crust. They are formed from melting rocks from inside the mantle and the crust.
Magma rising through cracks from underground slowly cools and forms the igneous rocks. These rocks, composed of minerals have fairly large crystals called, intrusive igneous rocks.
When the magma erupts through a volcano as lava, it cools at a different rate and creates, extrusive igneous rocks with smaller crystals. A third form created when lava cools at a rapid rate is an amorphous material and forms without crystals.
Once these rocks come to the surface, they are exposed to erosion and weathering. They are moved about by winds and water and over time layers of sediment build on them. With pressure from upper layers causing the sediment to compact and with other physical and chemical changes, the sedimentary rock is formed.
When intrusive magma is present, or a larger tectonic plate interaction occurs, the igneous and sedimentary rocks are put under extreme pressure and heat. This interaction results in the formation of metamorphic rocks. This result is how sandstone becomes quartz, limestone becomes marble, and serpentine becomes jade.
It takes a specific combination of five elements for the formation of each variety of gem; pressure, temperature, chemical elements, time, and space. This specific combination coming together for their formation is what makes gems rare.
Mother Nature has created many sub-cycles and cross interactions to occur in the formation of rocks which in different forms become gems. This is one method of their formation, others come from interactions with precipitation and other natural occurrences. It is an explanation of how they have become precious, even those considered semi-precious.