GARNET

Definition

garnet: Any of a group of silicateminerals that conform to the generalformula A₃B₂(SiO₄)₃. The elementsrepresenting A may include magnesium,calcium, manganese, andiron(II); those representing B mayinclude aluminium, iron(III),chromium, or titanium.

Industrial uses

Garnet is a general name for a group of mineralsvarying in color, hardness, toughness, and method of fracture, used for coating abrasivepaper and cloth, for bearing pivots in watches,for electronics, and the finer specimens forgemstones. Garnets are trisilicates of alumina,magnesia, calcia, ferrous oxide, manganeseoxide, or chromic oxide. The general formulais 3R″O·R₂O₃·3SiO₂, in which R″is calcium,magnesium, iron, or manganese, and R″is aluminum,chromium, or iron.
Garnet-coated paper and cloth are preferred to quartz for the woodworking industries,because garnet is harder and gives sharper cuttingedges, but Al₂O₃ is often substituted forgarnet.
Synthetic garnets for electronic applicationare usually rare earth garnets with a rare earthmetal substituted for the calcium, and iron substitutedfor the aluminum and the silicon.Yttrium garnet, is thus Yt₃Fe₂(FeO₄)₃.Yt–Algarnets of 3-mm diameter are used for lasers.Gadolinium (Gd) garnet has been chosen formicrowave use. Gd–Ga garnet made from GdOand GaO is used for computer bubble memories.