Fire Opal

Like precious and common opal,fire opal is hardened silica gel and usually contains 5 to 10% water in submicroscopic pores. A transparent to translucent variety of opal,fire opal usually does not exhibit color play unlike precious opal. For this reason,it is sometimes called jelly opal. However,a few Mexican stones shows a bright green flash. Fire opals are prized for their rich colors, such as yellow,orange,orange-yellow and red. Transparent specimens are usually faceted and often set into silver jewelry. Fire opal is found in sedimentary rocks such as sandstone and ironstone. In Mexico,a prime source of fire opal, it is filling cavities in rhyolite. Fire opals from mexico are sometimes sold as Mexican fire opals. Mexican opals are sometimes cut en cabochon with the opal resting in the center of its rhyolite host. Structure:Armorphous. Hardness:5-6 Specific Gravity:1.9-2.3 Refractive index:1.37-1.47 Luster:Vitreous. This ore can be Round brilliant or Cabochon shaped. Gem book.