Opal is a hardened silica gel, which generally contains up to 10% of water. Unlike other gem minerals opal has no crystalline structure and hence, it comes in amorphous shapes. Opal presents two varieties, which have been categorized as “precious opal” and “common opal”. The precious opal exhibits flashes of color when it is moved from one angle to other angles. On the other hand the common opal or “potch opal” is generally opaque and has no play of color. The play of color in the opal is due to a regular arrangement of tiny silica spheres, which diffracts the light.

Locations:

Opal has been mainly coming from Australia, which has been the major producer of opal since the 19th century. Other localities for opal are USA, the former Czechoslovakia, Mexico, Brazil and southern Africa.

Chemical Composition: Hydrated Silicon Dioxide
Crystal Structure: Amorphous
Hardness: 6
Specific Gravity: 2.10
Refractive Index: 1.37-1.47
Color: Colorless, white, milky blue, gray, red, orange, yellow, green, brown and black.
Luster: Vitreous

Astrological Relevance:

Opal is considered as one of the birthstones for the month of October, which covers two zodiac signs: Libra (September 22 To October 23) and Scorpio (October 23 To November 21).