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Opal


 

The word Opal comes from the Latin word "opalus," which means precious stone. Opal is a form of non-crystalline quartz, which is created from silica-bearing waters. When the silica solidifies, it creates the gemstone Opal, which contains 6 to 10 percent water. Opal is commonly found near geysers and hot springs, but it can occur in almost any geological environment.


When warmed by the hand, water contained within an Opal stone can change its colors, making them particularly brillant. Opals can be dehydrated when exposed to heat or chemicals. Many chemicals can damage an Opal due to its porous structure.

Scientists have been able to reproduce synthetic Opal in a laboratory, and other "simulants" exist on the market. Simulants are man-made stones which are simular to Opal but made from a different material.

Chemistry

Crystal System

Hardness
 SiO2.nH2O  None  5.5 - 6.5

Cleavage

 Fracture

Specific Gravity
 None  Conchoidal  Variable (1.8 - 2.3)

Color, Transparency
& Lustre

 VARIETIES 

Transparent to milky white appearing in white, grey, red, brown, blue, green & black.

Lustre: Most Opal has a vitreous (glass-like) or pearly finish, but some are resinous or dull.

 Common Opal:  Translucent, pale in various colors, but lacks the reflective colors of precious Opal.
Precious Opal: Milky white or black in color with reflections of brilliant colors such as, blues, reds & yellows.
Fire Opal: Red and yellow colors are dormant which create flame-like reflections.
Hyalite: Has no color.
Hydrophane: Becomes transparent when placed in water.
Wood Opal: Is wood that has been partially replaced by Opal silica.