From the finest robin's egg blue to dull greys and yellows, turquoise exhibits a extensive range of colours. It's scarce too, found only in dry, barren regions where it forms in a sedimentary process, groundwater seeping downward and reacting with minerals to form this porous, opaque stone. Usually it's judged on three qualities; colour, texture and the presence or absence of matrix; that is the spider's web tracery of dark lines demonstrating the rock that it forms in. Top colour is an even, intense medium blue, with a fine texture that leads to a good polish. Turquoise is a porous stone, so the vast majority of material is impregnated with colourless oil or polymer. In the past, Persia was the source for top quality turquoise, and 'Persian blue' is still regarded as the best colour. Now the mines are exahusted and it is China that supplies the highest quality material to the market. The majority of turquoise, however, still comes from the Southwestern US. The material I carry is from the US, and is a fine, turquoise blue. It is stabilised.