Silicon dioxide + hydration
(Crytocrystalline quartz pseudomorphed after wood)
SiO2 . H2O
AKA: Opal, Opalized Nature, Petrified Wood
System: None; usually massive, botryoidal, reniform, stalactitic, earthy.
Appearance: Replacement of cell structures preserves original wood texture in agate or opal. White, yellow, red, pink, brown, green, gray, blue, colorless; often shows rich internal play of colors (opalescence); pearly; streak white.
Physical properties: Hardness: (5.5 - 6.5); Specific gravity: (2.0 - 2.2). Cleavage: none, usually massive, botryoidal, reniform, stalactitic, earthy; fracture, conchoidal, conspicuous when compact; transparent to translucent; fluorescent.
Similar species: Dense opal resembles quartz, but it is softer and has a lustrous conchoidal fracture.
Occurrence: Opal is a low-temperature mineral and usually develops in a wide variety of rocks as cavity and fracture fillings. It frequently develops as amygdules in basalt and rhyolite of volcanic rock and replaces the cells in wood and the shells of clams. Common opal is widespread and can be readily obtained at many places, but localities for precious opal are rare and seem to be localized in W United States and Mexico. Magnificent examples of opalized wood can be found in Idaho, Nevada, Oregon, Utah, and Washington, and a lively green fluorescing opal (hyalite) occurs in New England and North Carolina and in cavities in basalt near Klamath Falls, Oregon.
Miscellaneous: Play of colors depends upon interference of light and is not dependent upon body color. Most opal is fashioned into cabochons. Very fragile, partly because when exposed to air it loses water and becomes filled with tiny conchoidal fractures (crazing). The name is from the Sanskrit upala, meaning "precious stone."
Conventional Wisdom: Acts to assist one in progression toward ones destiny. It further provides an impetus to actions which will advance one in the quest for the serenity which is inherent in all life.
Belongs to the Astrological Sign of Leo.