Opal
Opals are loved by many for their beautiful iridescence (flashes of colour). They have a similar composition as the mineral Quartz however they are not actually quartz, but hydrated silicon dioxide.
While some opals have amazing flashes of colour and are very vibrant, some have no colour and are simply back or white, however these are still opals. There is a variety called fire opal which is semi-opaque and yellow to bright orange in color.
There are many factors which add to the value of an opal. Black opals are considered more precious than light opals. However opals which feature iridescence vary in value according to the spread of colours, (this should be even throughout the stone with no clear patches.) it is also down to which colours are present, the most valuable being ones that feature all colours including red which is the rarest.
Many cultures regarded the opal unlucky, but nowadays it is considered a rare and precious gemstone. However there are also synthetic opals on the market, but any good jeweller should be able to tell these apart.
Opal is regarded as the traditional birthstone for October.
Many large opals have been found, one of the most famous is the Olympic Australis in Australia. It weighs 17,000 carats, and due to its purity it is estimated a gem upwards of 7000 carats could be cut from it. However due to its uniqueness it will probably be kept intact. It is valued at around AUS$2,500,000.
