Opal exhibits a variety of vibrant colors on its surface which is a result of light being diffracted off of tiny, closely packed silica spheres inside of the stone. Opals are frequently cut into cabochons with freeform shapes.
There are several types of opals:
|Precious white opal|
|Precious black opal|
|Precious jelly opal (Semi-black opal)|
|Common potch opal (Honey opal)|
|Common opal (Prase opal)|
|Common opal (Seascape opal)|
Harlequin opal, Ethiopian opal and crystal opal are very expensive types of opal. Andean opal is very popular because of its turquoise color. Honey opal is inexpensive and is often used for beaded jewelry. Color also plays a factor in the pricing of opal. The better and more even the color, the higher the value of the opal. The most expensive colored opal is red and the least expensive colors are yellow, green and blue.
The biggest source of opals is Australia.
Hardness: 5.5-6.5 Mohs
Specific Gravity: 1.98-2.50
Refractive Index: 1.37-1.52
Crystal Form: Amorphous. It's composed of hydrated silica gel and acts as a petrifying agent.