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

External links

corundum structure in 3D:

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