ANDRADITE

A rarer member of the garnet family. It is a silicate and measures 6.5 on the mohs scale. Some samples may contain inclusions of titanium or chromium. The finest specimens are usually green. It is named after a Brazilian mineralogist J.B. d'Andradae Silva.

The finest specimens are usually green and it was previously known as lime-iron garnet. It's most valuable form is demantoid which is green due to the presence of chromium. Other varieties include topazolite (yellow) and melanite (black/dark red).

It may be found in the Ural mountains, California, New Jersey USA.

ARAGONITE

A carbonate of calcium. It is fairly soft (3.5-4 on the mohs scale) and may be white/grey or colourless. It has the same chemical formula as calcium carbonate (CaCO3) but is rarer.It is also harder and has a different crystal structure and is harder.

It is often used for jewellery and is named after Aragon, the region of Spain where it was first found.

It is very widespread but found mostly in metamorphic and sedimentary rocks. It can be found in Austria, Cumbria UK, Aragon (Spain) and South Dakota (USA).