Thursday, May 12, 2016

Gemstone Origins: Natural Gem Formation

In a previous post, we talked about how gemstones are commonly manufactured in a lab setting. But have you ever wondered how gems are formed naturally? The process of gem formation is complex and requires various intricate chemical reactions, some more rare than others. The rate at which these reactions occur, and how common such an event is, will ultimately determine the value of the gemstone once it is mined.







Gemstone Origins
Most gemstones are formed in the top layer of the earth, called the crust. A few, such as diamonds and peridots, are formed in the mantle. All gemstones fall into at least one of three geological categories: igneous rock, metamorphic rock or sedimentary rock. Some gemstones are associated with more than one of these categories.


Igneous Rocks

Igneous rocks are created when magma from the earth's mantle rises and then cools slowly in the crust. This slow cooling can result in crystals which form minerals. As water near the earth's surface interacts with the minerals in the earth, certain types of gemstones are created. The types of gemstones created are determined by which type of mineral water has interacted with. For example, sandstone, which is rich in silica, is the basis for gemstones like amethyst and opal.
Other gemstones commonly associated with this process are diamonds, citrine, emerald, aquamarine, garnet, moonstone, topaz and zircon.

Sedimentary Rocks

When igneous rocks reach the surface of the earth, they are subjected to weathering and erosion which causes a breakdown into smaller particles. As time passes, these small particles build up in layers, either on land or in water. The resulting pressure causes lower layers to become compacted and undergo chemical changes which result in the formation of crystals from salts. The crystals form a bond which cause sediments to bond together, literally referred to as "cementation". The process takes millions of years, and eventually new types of stones are formed.
Gemstones commonly associated with sedimentary rock formation include jasper, sapphires and rubies.

Metamorphic Rocks

If sedimentary or igneous rock come into contact with magma through volcanic activity or shifts in tectonic plates, they are subjected to intense heat and pressure which can cause changes in the
All metamorphic rocks are created through heat, pressure and interactions with solutions through complex chemical processes.
Beryl, jade and lapis are just a few of the gemstones which can result from this type of interaction. In very rare cases where pressure is intense enough, diamonds can also be formed through this process.
existing rock's chemistry and result in the creation of a metamorphic rock. This type of contact us referred to as “metamorphism”.



As you can see, minerals and rocks are always in a state of change, moving through a continuous cycle that produces a variety of commonly-known gemstones. These constant changes are referred to as the "rock cycle", which is the cycle that ultimately determines the harness, shape, color and refractive index of all gemstones.

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