Chrysoprase is a form of chalcedony (micro-crystaline silica) that has been colored green by trace amounts of nickel when it was formed. It is found in a number of localities around the world usually coincident with nickel deposits but the most famous comes from an area in Australia known as the Marlborough mine. This material is very hard/durable and has a very pleasing blue/green color that is so prized in Asia that most of the Marlborough mine’s production goes into jewelry sold in China. In recent years, a deposit was found in Tanzania but I have found that very little of this material has the color and clarity necessary to be considered gem grade.