Opal gemstone base colors are colorless, orange, green, gray, black, brown, yellow, red, and purple. Some opals are made up of different colors that can be viewed from all different directions also when its turned or the light source is moved around.
This is called “play of color” which gives a stone color flashes or schillers of many different iridescent colors that may vary in different stones. Opals play of colors is unsurpassed and quite exceptional to behold. This is termed opalescence. The colors or schillers may be large, or tiny dense flashes of colors. The value of opal is determined by the intensity and distribution of color flashes.
There is a condition called crazing in certain opals that causes the stone to form cracks. This happens when opals are removed from damp conditions and dried too quickly, or when exposed to sudden intense light or both. Vibration can cause crazing caused from the polishing and cutting of the stone. Severity of crazing and time taken ” to craze” varies among the different specimens of opal. Origins of specimen determine its resistance to crazing.
Gradually drying over months or years can in some of the cases stabilize the stones. This allows them to be cut, polished with highly reduced risk of crazing occurring.
Opals that display play of colors are considered precious opals. Opals with out play of colors are considered common opals. Gems are cut from both types of opals, although precious opals are known as the gem form of the stone.
Many varieties exist of both common and precious opals. One of the most desirable of all opals is black opal. Black opal has dark blue, dark green or black background with strong play of colors. The next desirable opal is the white opal which has a light color body, which can be white, yellow, or cream with a strong play of colors.
The Mexican Fire Opal is a transparent to translucent orange red color and a common opal. Mexican Fire Opals that display play of color are considered Precious Fire Opal.