Green sapphire is made through natural geological processes involving heat, pressure, and specific trace elements present during its formation.
Sapphires, like all corundum gemstones, form deep within the Earth's crust. The presence of iron (Fe) in the crystal structure of corundum (aluminum oxide – Al₂O₃) causes it to appear green. Here's a more detailed breakdown:
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Natural Formation: Green sapphires, like other sapphire colors, form over millions of years under intense heat and pressure. This commonly occurs in:
- Metamorphic Rocks: These rocks are formed when existing rocks are transformed by heat, pressure, and chemically active fluids. Sapphires can crystallize during this metamorphic process.
- Igneous Rocks: These rocks are formed from the cooling and solidification of magma (molten rock). Sapphires can crystallize from magma as it cools.
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Key Elements:
- Aluminum Oxide (Al₂O₃): This is the base material for all sapphires.
- Iron (Fe): The presence of iron is essential for producing the green color. The specific shade of green depends on the concentration of iron present.
- Other Trace Elements: While iron is the primary colorant, other trace elements can influence the overall color and hue of the green sapphire.
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The Process:
- Molten or Dissolved State: Aluminum oxide, along with trace elements like iron, exists in a molten state within the Earth's crust or is dissolved in hydrothermal fluids.
- Crystallization: As the molten material cools or the fluids change temperature and pressure, the aluminum oxide starts to crystallize into corundum.
- Incorporation of Iron: During crystallization, iron ions are incorporated into the corundum crystal lattice.
- Formation of Green Color: The iron absorbs certain wavelengths of light and reflects others, resulting in the perception of a green color.
- Geological Activity: The sapphire-bearing rocks are then brought closer to the surface through various geological processes like volcanic eruptions or tectonic uplift.
It's important to note that some sapphires are heat-treated to enhance or alter their color. While this process can improve the color of a naturally occurring green sapphire, it doesn't create the sapphire itself. The green color must be fundamentally present due to the iron content from its original formation.
