Calcite, coloured by iron oxide

Calcite

A very common stone, a component of limestone, marble and lapis lazuli.

It occurs in many marbles and very popular for carvings. Red and orange tinted calcite is coloured by iron oxide.

Cassiterite, sometimes confused with diamond

Cassiterite

Tin ore, cassiterite gets its name from Greek for 'tin' which came from the Sanskrit word 'kastira' and most often found as small black crystals, sometimes collecting in river gravels where it can be panned in the same way as gold.

Less often cassiterite occurs as larger crystals with an adamantine appearance, which means the paler crystals are sometimes mistaken for diamonds.

Reddish-brown crystals tend to be lower priced at around £20 - £50 the paler yellow crystals cost considerably more.