How are opals formed?

Opal boulder found in Queensland forms in a slightly different method to other types of Australian opal, forming inside an ironstone concretion. The concretion was formed due to ionisation from sedimentary deposition. The Idaho Spencer opal mines in the USA the Opal Solution or silica, was a secondary deposit carried by geyser activity. read more

Opal is a non-crystalline form of the mineral silica and is formed from amorphous "balls" or "lumps" of silica. So the opal is a very unique gem compared with others, like diamonds or a ruby which is formed crystalline. read more