How are Australian Sapphires formed?
Sapphires, like other corundum gemstones, are formed deep within the Earth's crust through a combination of heat, pressure, and mineral interactions over an extended period. Here's a simplified explanation of the process:
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Origin: Sapphires are primarily composed of aluminum oxide, known as corundum, with trace elements giving them their distinct colors. Blue sapphires, for example, typically contain iron and titanium.
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Heat and Pressure: The formation process begins in the Earth's crust, where extreme heat and pressure cause the aluminum oxide to crystallize into corundum.
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Magma and Metamorphism: Sapphires can form in igneous rocks like basalt or in metamorphic rocks under high pressure and temperature conditions. During volcanic activity, magma brings corundum-bearing minerals to the surface.
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Mineral Inclusions: As the corundum crystals form, they can incorporate various mineral inclusions, which contribute to the sapphire's color and sometimes create the sought-after "star effect" or asterism seen in star sapphires.
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Cooling and Crystallization: Over time, the molten rock cools, allowing the corundum crystals to solidify. This slow cooling process is crucial for the development of larger, well-formed crystals.
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Secondary Deposits: Sapphires are often found in secondary deposits, like riverbeds or alluvial deposits, where they have been transported by erosion from their original formation sites. In these secondary deposits, miners can extract the sapphires from gravel or sediment.
It's important to note that the exact conditions and geological processes can vary, leading to the diversity of sapphire deposits worldwide. The unique colors and characteristics of sapphires are influenced by factors such as trace elements, the presence of other minerals, and the conditions during their formation.
