|Types of opal|
Photo: Amazing Geologist page on facebook
Opal is a hydrated amorphous form of silica (SiO2·nH2O), Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.
It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.
Precious Opal - is opal which exhibits the phenomenon known as play of colour, which is produced by the diffraction of white light through a micro-structure of orderly arrayed spheres of silica.The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors.
The variety of natural opal is determined by the two characteristics of body tone and transparency.
Body Tone - The base tones of light, dark and black opal range from colourless, white, through the various shades of grey, to black.
Transparency - Opal of any body colour will be opaque, translucent or transparent. When it is transparent or very translucent, and the colour clarity is sharp, it is often referred to as crystal opal.
Types of Natural OpalsThere are many different types of natural opals. There is black opal, white opal, crystal opal and jelly opal. There are other kinds - fire opal, hyalite, water opal, hydrophane and honey opal.
|Natural Black Opal (OPAQUE) Indonesia. credit : Nur Rachman Effendi|
|Boulder Opal Specimen by Dieter Rosenkranz Australia|
|Incredible Fire Opal From Mexico. |
|Matrix opal , From Queensland Australia|
|Hyalite, from Megyaszó (Hungary). Copyright: Stone Ásványfotós|
Girasol opal is a type of hyalite opal that exhibits a bluish glow or sheen that follows the light source around.
|⚒ Stunning Blue Green Peruvian OpalPhoto : © Trudi Unsworth|
|Bright honey opal from hungary|
Honey-yellow, translucent to clear and resinous to glassy in appearance. It may or may not have play-of-colour.
White Gilson Snythetic Opals
|Stunning Mexican Fire Opal looks like a beautiful sunset in the|
clouds or a fiery explosion with billowing smoke. Photo: Jeff Schultz
|The Eagle Opal - 50 carat contra luz precious opal from Oregon, USA|
|Outstanding Rough Opal From Oregon, United States.|
|The Oregon Opal with the Ocean inside|
Credit: Mckenna Praetorius
|Oregon Contra Luz Opal with botryoidal Jasper inclusions, from Oregon|
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