Corundum
 | Al2O3Al₂O₃
These samples of corundum are displayed in the Smithsonian Museum of Natural History. Corundum is a oxide mineral of aluminum with the composition Al2O3. The sample at left is about 6 cm across and is from Franklin, New Jersey. 这些刚玉样本陈列在史密森尼自然历史博物馆中。刚玉是一种铝的氧化物矿物，化学式为Al₂O₃。左侧的样本宽约6厘米，来自新泽西州弗兰克林。
Pure corundum is colorless, but the addition of a small impurity of chromic oxide can make the precious stone ruby (red) and the addition of titanium oxide can make sapphire (blue and other colors). From the Museum of Natural History description "Corundum rarely has the clarity or richness of color to be a gemstone. When it does, the difference between a ruby and a sapphire is just a tiny bit of impurity." 纯刚玉是无色的，但加入少量铬氧化物可使其成为红宝石（红色），而加入钛氧化物则可使其成为蓝宝石（蓝色及其他颜色）。根据自然历史博物馆的描述，“刚玉很少能具有足够的透明度和色彩 richness 来成为宝石。当它确实能时，红宝石与蓝宝石的区别仅仅是一点点杂质。
Corundum and impure corundum called emery are used in making abrasive cloths and wheels. Corundum is second only to diamond in mineral hardness. It measures 9 on the Mohs hardness scale, compared to 10 for diamond. 刚玉及其杂质较多的刚玉（称为刚玉石）用于制造磨布和磨轮。刚玉的矿物硬度仅次于钻石。它在莫氏硬度刻度上为9，而钻石为10。
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This sample of corundum is from Franklin, New Jersey and is about 10 cm across. 这块刚玉样本来自新泽西州弗兰克林，直径约10厘米。
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Mindat: Corundum
| Minerals
矿物 |
| HyperPhysics*****Geophysics
HyperPhysics ***** 地球物理学 | R Nave |