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A sample of hyalite

Hyalite is a form of opal with a glassy and clear appearance which exhibits an internal play of colors and has natural inclusions. It is also called Muller's glass, water opal and jalite. The name Müller's glass derived from the name of its discoverer, Franz-Joseph Müller von Reichenstein. Its Mohs hardness is 5.5 to 6 and it has a specific gravity of 2.1. It is an amorphous form of silica (SiO2). Its has a conchoidal fracture, a vitreous luster and a white streak. It is sometimes mistaken for resin opal, since they both look like little globs. It glows bright green under blacklight. Hyalite's density ranges from 1.9 - 2.3. Its crystal structure is amorphous, meaning that it does not form crystals. It has no cleavage. Hyalite is used for jewellery, but it can be confused with glass until put under a blacklight. It is also a collector's gem because of its fluorescence. Hyalite, like all opals, forms through precipitation. Silica-laden water seeps through tiny cracks in rocks, depositing the silica for thousands and thousands of years as it forms an opal.

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