... sight glass; furnace sight glass.Substrate material,Project TV faceplate.Optical windows; optical lens; prisms; domes.A valve ... dolomite, corundum and garnets .Notable Occurrences include Burma, Sri Lanka, Brazil and Afghanistan.Best Field Indicators are twinned crystals ... a fondness for the varieties in question.In addition to Burma, spinel is mined in Sri Lanka, Tanzania, and Tadzhikistan, part ...