Hematite structure

It's a slightly nontrivial hexagonal crystal structure.

• Al₂O₃ Aluminium(III)_oxide - leukosapphire - (Sapphire and Ruby are colored variants) - 2,072°C - 3.987g/ccm - Mohs 9 (defining compound)
• Ti₂O₃ Titanium(III)_oxide - tristarite - 2,130°C (decomposes) - 4.49g/ccm - metallic luster - semiconducting to metallic at 200°C - Mohs 8.5
• Fe₂O₃ Hematite

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More rare elements:

• Cr₂O₃ eskolaite - 5.18g/ccm - Mohs 8 - metallic
• Mn₂O₃ manganese-bixbyte - 4.95g/ccm - Mohs 6 to 6.5
• V₂O₃ karelianite (webmineral) - Mohs 8 to 9 - metallic luster

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Way too rare elements:

• Tl₂O₃ avicennite - 8.9g/ccm - Mohs 2

External links

• Wikipediacategory: hematite group aka corundum group

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Corundum structure in 3D:

• at the materials project: [1]
• at www.mindat.org [2]
• at www.mineralienatlas.de [3]
• [4]
• corundum group minerals [5]