December-Turquoise

Colour	Blue
Formula	CuAl6(PO4)(OH)85H2O
Group	Phosphates
Uses	Jewellery and ornaments
Origins	Forms by water action on phosphate rocks containing Al
Locations	Earliest discoveries in Israel. Found in US, Australia, UK

Turquoise derives it's blue colour from copper. Green patches may be due to the presence of impurities, which may be absorbed because it is porous. These may reduce it's value. It is classed as semiprecious and is fairly soft (6 on the mohs scale). Wax and resin are sometimes added to improve it's appearance.

Turquoise is a secondary material found mainly in arid environments. In ancient times it was believed to be magical because it changed colour from blue to green. It looks like chrysocolla but can be identified as turquoise because this is harder.