Corundum is the crystalline alpha form of aluminium oxide, . Its strong bonded structure gives high hardness and chemical durability.
Salts or small amounts of impurity ions can alter its optical properties without changing the basic host lattice. Ruby and sapphire are gem varieties of corundum, demonstrating how composition at the impurity level affects color.
Sapphire is gem-quality corundum, crystalline , conventionally excluding the red variety called ruby. Trace impurities and defect centers can produce several colors.
Synthetic sapphire is also valued as a hard, optically useful substrate and window material. The material's structural identity is aluminium oxide; a color name alone does not specify which impurity or electronic transition is responsible.
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Corundum is a naturally occurring mineral comprised primarily of aluminum oxide (Al₂O₃). It is known for its hardness, ranking 9 on the Mohs scale, making it one of the hardest substances in nature. Corundum can take on various colors depending on the presence of trace elements, resulting in well-known varieties such as: 1. **Sapphire**: Typically blue but can come in many other colors except red.