Opal
Opal is a unique mineral because it forms as a
gel in cracks of many different types of rocks. However, opal is most often found in rocks like basalt, rhyolite,
sandstone and limonite. High water
content is a trademark of the opal. Up
to 20% of an opal can be water. Opals
come is a wide arienty of colors including white, reds, greens, pinks, browns,
and blues to name a few. Most opals do
not have a specific shape, however, “precious” opal which are used for jewelry
do have a round structure to them. Almost all of the world’s opal supply comes from Australia.