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Oval Opal Showing Attractive Flashes of Colour
Oval Opal Showing Attractive Flashes of Colour

Opal

Opal - Stone of Paradox
Opal is a paradoxical gemstone, and one of the most fascinating.
It is a form of quartz, but is not a form of quartz. Quartz is very common, yet has many rare and precious gem varieties. Opal itself has numerous varieties. It is the most colourful gemstone, but some forms are colourless. It can be very bright and beautiful, and it can be dull and dead. It is best known for its flashes of colour, but some varieties have no flashes of colour, and are still opals. It can be black, and it can be white. Its best known attribute, the brilliant flashes of many colours, are not called opalescence, but irridescence. Some people think opal is unlucky, but it is one of the most valuable and desirable of gems.

One of the Many Forms of Quartz
Opal is a variety of quartz. Quartz in turn is silicone dioxide, one of the commonest minerals on earth. Quartz exists in a number of different forms, ordinary sand is one form, but there are numerous gemstone forms of quartz.

Opal is a Gel
Actually because opal is a gel, it is, strictly speaking, not a form of quartz. Quartz is a crystalline form of silicon dioxide, opal is a solid gel. However because the chemical formula is the same except that opal is hydrous, that is it contains some water which is chemically attached to the silicon dioxide molecules.

The Most Colourful Gemstone
To follow (27th March 2001)

Roman Mines
Opals were known and mined in Roman times. The Roman mines were in and around Cervenica, previously in Czechoslovakia, although we have now lost track of all the recent changes in Balkan geography.

You may wish to check the attributes of gemstones on our Gemstone Characteristics page.

The hardness of opal is 5.5 to 6.5.

Synthetics
To follow (27th March 2001)

Misnomers
To follow (27th March 2001)

Technical Details
Chemical Composition and NameSiO2nH2O - Hydrous Silicon Dioxide
Hardness5.5 to 6.5
Refractive Index1.44 - 1.47
Specific Gravity1.95 - 2.20
Crystalline SystemGel
Other Optical PropertiesIsotropic



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