Opal 

Opal is the most special of the silica gemstones.

There are four types of highly prized Opal. They comprise the White Opal, which has a light or white body colour with a fine play of colour; the Black Opal, which has a black or dark blue, green or grey body colour with vivid flashes of colour springing from the dark stone; the Fire Opal, which is transparent to translucent with an orange-red to red body colour, which may or may not show a play of colour; and the Water Opal, which displays brilliant flashes of colour in a clear, colourless (water-white) stone.

The body colour may be black, grey, white, brown, pink, orange to yellow, green or bluish green, blue  or colourless. Some White Opals have a translucent, milky appearance, and it is this, not the play of colour, which is termed opalescence. The most important gem varieties are those showing a play of colour. They may be described as Black or White Opal, with these terms referring to the colour of the background against which the play of colour is seen. Black Opal is the most desirable.

Opals occur in cavities and fissures in rocks from low temperature, silica-bearing water. They are found in New South Wales, South Australia and Queensland in Australia, Brazil and the USA.

Most varieties are cut as cabochons, beads and carvings.

Fire Opal is obtained mainly from Mexico and may be faceted, often with a slightly domed table.

• Opal is the birthstone for October
• Opal is the Zodiac stone for Scorpio
• Opal jewellery is often given as a 14th Wedding Anniversary gift

View Opal Jewellery at Astley Clarke