Quartz occurs in both a crystalline and polycrystalline variety. Crystalline quartz consists of relatively large crystals that are usually visible to the unaided eye, while polycrystalline quartz is fine-grained and consists of masses of minute crystals.

Polycrystalline quartz: Chalcedony is a general term for translucent fine grained quartz, which is distinguished by a microscopically fibrous banded structure. The banding may be visible to a varying degree in most varieties, and is the most prized characteristic of agate and onyx.

Onyx

Onyx is a Chalcedony quartz that has a fine texture and black colour. However, some Onyx also displays white bands or ribbons against a black or brown background, and this variety can be known as Sardonyx.  Its name comes through Latin from the Greek ‘onyx’ meaning 'claw' or 'fingernail'. Legend says that while Venus was sleeping, Eros cut her fingernails and left the clippings scattered on the ground and, because no part of a heavenly body can die, the gods turned them into stone, which later became known as Onyx.

Cameos are often made from Onyx, with the figure carved in white in relief against the black background.

Onyx is mined in Brazil, India, California and Uruguay.
 

• Onyx jewellery is often given to mark the 7th Wedding Anniversary

View Onyx Jewellery at Astley Clarke