Hematite group

Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium, and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. Corundum has two primary gem varieties: ruby and sapphire. Rubies are red due to the presence of chromium, and sapphires exhibit a range of colors depending on what transition metal is present. A rare type of sapphire, padparadscha sapphire, is pink-orange.

Hematite (), also spelled as haematite, is a common iron oxide compound with the formula Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . It has the same crystal structure as corundum () and ilmenite (). With this crystal structure geometry it forms a complete solid solution at temperatures above .

chemical compound

Eskolaite is a rare chromium oxide mineral (chromium(III) oxide Cr2O3).

Karelianite is an rare mineral, a natural form of vanadium(III) oxide, V2O3. In terms of chemistry it is vanadium-analogue of hematite, corundum, eskolaite, tistarite, bixbyite, avicennite, and yttriaite-(Y). The name comes from Karelia, a region on the Finnish-Russian border. It may be associated with magnesium-rich rocks.