A lengthy bipyramidal crystal of ruby, a variety of the mineral corundum, is here seen embedded in a clear-white, quartzite host rock. Corundum is a shared name for the gemstones ruby and sapphire, the reddish purple variety in this sample being ruby. Corundum is an aluminium oxide mineral (Al2O3) of very high hardness (Mohs 9), used as an abrasive in industrial processes. Clear, translucent crystals are much in demand as semi-precious stone in jewellery.