FIRE AGATE

A form of chalcedony which is itself a compacted form of quartz. It is made up of one atom of silica and two of oxygen. It is white in it's pure form but can be different colours due to the presence of impurities (usually red).

It is moderately hard (6.5 on the mohs scale) but is slightly softer than chalcedony because it absorbs water like all forms of agate. Agate usually has bands on it's surface but fire agate is different. It has a rainbow like arrangement of surface colours. This is known as iridescence and may be enhanced by cutting in a particular way. It is caused by fragments of iron oxide becoming lodged in the layers between crystals. Iron is not part of the chemical composition and therefore is classified as an impurity and does not appear in the chemical formula.

The finest samples are smoothed into beads.

Fire Agate can be found in igneous rocks and occurs in small rounded lumps of volcanic lava where it usually forms in layers that line a cavity (a geode).

It can be found in Brazil, Mexico, India, South Africa and Arizona (US).

FIRE OPAL

A form of silica which is a member of the oxide group. It is usually orange, red or yellow and acquires it's distinctive colouring from the the presence of inclusions, particularly iron. The finest samples are a rich orange colour throughout.

It is a solidified gel with no crystal structure and is therefore amorphous. The finest samples if revolved in the hand create a fire like light which is where it gets it's name from. It is moderately hard (6 on the mohs scale).

It is limited in it's use as a gemstone due to it's water content (up to 10% of it's weight) and it's sensitivity to heat. It decomposes when heated and sometimes turns into chalcedony and quartz.

It usually occurs in tiny pieces which are embedded in rock. Therefore it is usually too small to be moved and used for jewellery. Many fire opals may be surrounded by bands of agate. Agate contains the same chemical elements but does not have crystallized water attached to it.

Most opal is deposited from silica rich waters in sedimentary rocks around geysers and hot springs. It mostly forms in these conditions where there are veins of iron and magnesium bearing minerals.

It can be found in Mexico, Australia, Czech Republic, Sardinia, Romania, and Yellowstone Park (US).