Hyalite
Encyclopedia
Opal
Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...
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. Its Mohs hardness is 5.5 to 6 and it has a specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
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.
The name Müller's glass derived from the name of its discoverer, Franz-Joseph Müller von Reichenstein
Franz-Joseph Müller von Reichenstein
Franz-Joseph Müller Freiherr von Reichenstein or Franz-Joseph Müller von Reichenstein was an Austrian mineralogist and mining engineer. Müller held several positions in the Austria-Hungarian administration of mines and coinage in the Banat, Transylvania, and Tyrol...