The name mineral springs from the Greek name "opallios" and from the Indic "upala", which means "Precious Stone". it's completely different from most precious gems attributable to its non-crystalline crystal system, or amorphous, in nature. Blue opal is allochromatic and comes in an exceedingly sort of colours, the foremost valued being black. different forms embody white (milk opal), red (fire opal), or colorless (water opal). the foremost placing options of precious mineral area unit the radiance effects it exhibits once turned within the lightweight, called "play of color". this is often caused by minute spheres of silicon dioxide that replicate and separate white lightweight. This result is understood as "opalescence". Smaller spheres manufacture solely blues and greens, whereas larger ones manufacture the entire spectrum. Black opals highlight play of color most dramatically. Opal rings for women look superb in straightforward jewellery settings and appearance significantly engaging, after they area unit set in rings.
Identification:
Opal encompasses a hardness of five.5 to 6.5 and relative density of two.1 to 2.2 and encompasses a tenuity. it's clear to opaque, encompasses a vitreous, greasy, dull, or waxy luster, and leaves a white streak. it's one by one refractive, and it's porous. during this case, it's dangerous to immerse it in any liquids apart from water.
Occurrence:
One space of former geographical area erst happiness to European country has been mining mineral since Roman times and was the sole supply of noble mineral to Europeans. In times, most opals area unit coming back from Australia wherever the best quality opals area unit found. different sources area unit principally North American country, Guatemala, Honduras, u. s. and Iceland.
Varieties:
There area unit few varieties, however principally there area unit three varieties that area unit hottest in gem business area unit follows: White Precious mineral, Black Precious mineral and {fire mineral|girasol|opal} and conjointly known as common opal. each has its own distinctive colours and characteristics.
Value:
An opal's worth depends on its body color, play of color, and soundness. there's no comparison between the worth of noble mineral which of fireside mineral, that is sort of cheap even compared with different minor gems. it's value somewhat a lot of once a number of splashes of color area unit visible within the stone. it's valued by collectors as a curiosity however is no employed in jewellery. A opal, free from flaws and with the same pattern created from bright clear colours, as well as red, is also value a lot of per carat than diamond. Common opals don't exhibit play of color and, as a result, area unit worthless.