Is opal igneous sedimentary or metamorphic?
Is opal igneous sedimentary or metamorphic?
Opal is found as two types: volcanic opal which infills vesicles and cracks in igneous rocks, and the more familiar sedimentary or sandstone type which is found in Australia’s main fields. Most deposits in other countries are volcanic opal, much of which is prone to crazing.
What kind of rock does opal come from?
sedimentary rocks
Much matrix opal is found in sedimentary rocks such as sandstone, limestone, chert, or ironstone. In these rocks precious opal has precipitated within the interstitial spaces between sedimentary particles. In some cases it replaces sedimentary material.
How is an opal formed?
Opal is comprised of tiny silica spheres, formed when silica-rich water seeps into deep cracks and voids in the Earth’s crust. It is separated into two groups, common opal (also known as potch) and precious opal (also known as noble opal). A cross section of opal in its host rock.
Is opal a mineral or rock?
mineraloid
Opal is a mineraloid because it is amorphous hydrated silica. Despite its mineral-like properties, opal’s chemical structure is hydrated with varied water concentration. Because of this variance, the stone’s structure isn’t fixed or organized and thus, qualifies as a mineraloid.
How do I know if I have an opal rock?
Most genuine solid opals have an irregularity in this area – curved or bumpy due to their natural formation – whereas a man-made stone will be perfectly flat because the two sections are flattened so they can be glued together. Be especially wary if the opal is set in jewellery and you cannot see its back or side.
Where is the best place to find opals?
It’s clear that Nevada is the best place to find opal in the US, thanks to the world-famous Virgin Valley opal, a remote, fruitful mining district supplying some of the world’s finest black opals.
Do all opals fluoresce?
Most opal will fluoresce weakly under an ultraviolet lamp. However, some specimens are strongly fluorescent. One locality that yields opal with very strong fluorescence is Virgin Valley, Nevada, from which many specimens will glow with a spectacular green fluorescence.
