What is "hyalite"

Opal \O"pal\, n. [L. opalus: cf. Gr. ?, Skr. upala a rock, stone, precious stone: cf. F. opale.] (Min.) A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.

Note: The precious opal presents a peculiar play of colors of delicate tints, and is highly esteemed as a gem. One kind, with a varied play of color in a reddish ground, is called the harlequin opal. The fire opal has colors like the red and yellow of flame. Common opal has a milky appearance. Menilite is a brown impure variety, occurring in concretions at Menilmontant, near Paris. Other varieties are cacholong, girasol, hyalite, and geyserite.

n. (context mineral English) A form of opal.

Hyalite is a form of opal with a glassy and clear appearance which may exhibit an internal play of colors if natural inclusions are present. 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.