Boulder Opal comes from Queensland in Australia. It is composed of two parts: host rock, which is usually an ironstone or sandstone and a precious opal. It was created when silica bearing water penetrated rocks and deposited opal in the cracks. Opal veins in ironstone tend to be thin, while the host rock is very hard. That’s why most opals from Queensland cannot be detached and must be cut in this particular way.
Boulder Opal becomes increasingly popular because of the attractive patterns it forms with the host rock and the strong colours it shows. Ironstone provides very good contrast to the play of colour and has a nice brown colour with swirling bands of darker and lighter hues. Against this type of background opal’s fire shines extremely well. A quality Opal from Queensland can rival famous Black Opal in terms of appearance. There are two major varieties of this gemstone. One is called Matrix Boulder, where cut gemstone shows a network of opal patterns in the host rock. The other one is full faced Boulder Opal where it was possible to cut it in such a way, that no host rock is visible. The second type is more expensive of course but the Matrix variety is also very attractive.