We already covered opals in a birthstone post, but this week we want to focus in on the more technical aspects of this unique stone: the different types, colours, and where in the world they can be found.
Opal is made when rain soaks into very dry, desert-like ground, like you find in the outback of Australia. This water soaks down deep into the rock below, taking with it something called silica, a dissolved mix of silicon and oxygen (from the air). When the rains stop, and the water in the ground has evaporated in the heat, deposits of this silica are left in between layers of rock – forming opals, with their rainbow of colours.
Opal can be categorised into many different categories, but the main groups of opals you are likely to come across are called the following:
White opal: this type of opal is translucent to semi-translucent (meaning light passes through it, highlighting its colours) and often flashes of colour can be seen against a background of white or light grey.
Black opal: the black opal can be translucent or opaque, and is the same as above except with a black background to the stone.
Boulder opal: boulder opal features its colours against a light to dark background, but parts of its surrounding rock have become part of the finished gem – hence the name.
Matrix opals are one kind of boulder opal, found in a ‘host rock’, through which deposits of opal run.
Crystal opal: crystal opal is completely transparent to semi-transparent (meaning you can see through it), with a clear background. Because of its transparency, this stone can feature extraordinary flashes of colour.
The best opals in the world are found at Lightning Ridge, Australia, and have been being bought from there since the 1800s.Ethiopia is also a source of some very beautiful opals, but because of their formation they can change to become milky, so buyers should be aware of this when purchasing an Ethiopian opal.
Another thing that buyers should look out for when choosing their opal, or piece of opal jewellery, is whether the opal they are looking at is solid stone, or something called a doublet or triplet opal. Doublets and triplets are slices of opal, attached to a black backing and then, in the case of a triplet, affixed with a clear dome. These are cheaper than solid opals as they contain less stone, and can still be striking – however, here at Origin31, we don’t use these as we feel that stones should be kept as nature intended.
You can normally tell if your opal is a doublet or triplet by looking at its side; if the stone has been attached to a backing with glue then the join will be completely flat. This can be tricky when the stone is already set in jewellery.
Take a look at our collected of jewellery using always solid opals, or get in touch with us to talk about making that perfect piece of custom jewellery – after you’ve read through this post and chosen your favourite type. We’d love to work together.