BOULDER OPAL ROUGH GEM
Boulder Opal Rough Gem. An Opal specimen in dreamy green and blue spectrum of colour. A really lovely piece of Aussie stone. This top specimen is a feature piece with attitude from quality Boulder Opal gemstone. You can see gemstones could be cut from just the exposed face here, and who knows what is in the seams of this rock. Photos are taken with dry stone, outside.
7.6cm x 6.5cm x 6.8cm, 386g.
Opal: SiO2 · nH2O Hydrated Silicon Dioxide.
Boulder Opal is a variety of Precious Opal found in Queensland, Australia, as cracks or coatings in and around ironstone/sandstone boulders. Opal has been a popular gem for many centuries and has a very interesting structure. The name opal probably is derived from the Sanskrit name for precious stone- upala.
Opal is considered a mineraloid because this structure is not truly crystalline. The chemistry of Opal is primarily SiO2 and varying amounts of water. The amount of water varies from 5 -10% and greater. This water can help geologists determine the temperature of the host rock at the time the opal formed.