Corundum

Al₂O₃

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Second in hardness only to diamond, corundum is an aluminum oxide (Al2O3) with a Mohs hardness of 9. Its gem varieties are ruby, colored red by chromium, and sapphire, which covers all other colors. The mineral crystallizes in the trigonal system as tabular, prismatic, or bipyramidal crystals with an adamantine luster, a colorless streak, and no cleavage. Specific gravity ranges from 3.98 to 4.10. Corundum's extreme hardness makes it a widely used abrasive, and synthetic corundum serves in laser technology, while the finest natural crystals are cut as ruby and sapphire. Colors other than red span the full range of sapphire, from blue and yellow to pink and colorless.

Corundum is the second hardest natural mineral after diamond. Its gem varieties are ruby (red, colored by chromium) and sapphire (all other colors). Synthetic corundum is widely used as an abrasive and in laser technology.

ระบบผลึก	Trigonal
หมวดหมู่แร่ธาตุ	04 Oxides and Hydroxides
ความแข็งโมห์ส	9.0
ความถ่วงจำเพาะ	3.98-4.10
สี	Red (ruby), blue (sapphire), various colors
ความวาว	Adamantine
สีเส้นขูด	Colorless
การแตกเรียบ	None
รอยแตก	Conchoidal to uneven
ความโปร่งใส	Transparent
ลักษณะผลึก	Tabular, prismatic, bipyramidal