Opal

Opal, an amorphous form of hydrous silica, was once held to be unlucky, but maybe this was only because the stone is rather fragile and tends to chip and scratch easily. As it contains a high percentage of water, opal may deteriorate in heat and cold. Nonetheless, it is a very beautiful stone and, without wishing to contradict myself, it is even used as a lucky charm in certain countries.

There are numerous varieties of opal, each attractive in its own way. The harlequin opal, as the name suggests, gives a rich play of prismatic colours flashing from minute fissures, even when cut en cabochon. It is translucent and spangled with many shades of red, blue and yellow specks.

Common opal is a dull white or milky blue colour and produces the same effects but to a lesser extent due to its opacity.

Fire opal is hyacinth-red to honey-yellow and shows intense orange and red fire-like reflections. It is the only variety that can be faceted, as some specimens are totally transparent.

Water opal is similar to fire opal, but is colourless.

Wood opal is due to the replacement of fossil wood by hydrous silica with perfect retention of the woody structure. It is cut with its matrix remaining for added strength.

Precious opal, if held to the light, shows a marvellous display of brilliant colours. It is the most prized of all.

Opal should be thickly cut due to its fragility, for the finer the cut, the more the stone will deteriorate in time. It is a good idea to wash opal in pure water every now and then so as to remove all traces of perspiration or cosmetics. In other words, opal is a good investment for the meticulous, less so for the negligent!

Even though extensive new deposits have recently been discovered in Australia, from which enough opal to virtually inundate the market could be mined, the price of this gem continues to rise.

Most opal comes from Australia, except for the fire opal which is found in Mexico.

Techinical Specification

Name	Moh's	Specific Gravity	Structure	Cleavage	Refractive Index	Double	Disp.	Pleochro	Fluorescence
Opal	5.5-6.5	1.98-2.20	Amorphous	None	1.44-1.46	None	None	None	Variable