Thursday, October 27, 2016

Fire Agate

Fire agate is a semi-precious variety of chalcedony found only in certain areas of Arizona, northern Mexico, and parts of the southwestern United States. During the tertiary period, about 24-36 million years ago, the area was subjected to massive volcanic activity. The fire agates were formed when hot water, saturated with silica and iron oxide, repeatedly filled cracks and bubbles in the surrounding rock.

The formations are botryoidal (grape-like) growths.
Fire agate gemstones have iridescent rainbow colours, similar to opal, with a measurement of hardness on the Mohs scale of between 6.5-7.

The vibrant colours found within fire agates are caused by alternating silica and iron oxide layers which diffract and allow light to pass. Thin limonite and/or geothite iron oxide layers cause light interference within the microstructure crystal layering of the gemstone, giving the fire agate its visual effects.