Volcanic glass

VOLCANIC GLASS (EN: volcanic glass; DE: vulkanisches Glas; FR: verre volcanique; ES: vidrio volcanico; RU: вулканическое стекло) is the amorphous volcanic rock, or the part of this rock, which is formed during the rapid (without the crystallization) congealing of the lava.

The volcanic glass is the supercooled liquid with the extremely high viscosity. During the congealing of the very viscous varieties of the acidic rhyolitic lava, which is containing the large quantity of the SiO2, there is formed the volcanic glass, which is called the obsidian. Less often, there congeal in the form of the glass the basaltic lavas, which are relatively poor in the SiO2, thus giving the dark opaque basaltic volcanic glass, namely, the tachylite. In the case of the congealing of the lava within the aqueous medium, there is formed the volcanic glass with the high content of the water (Pechstein, pitchstone). The porous volcanic glass is known under the name of the volcanic pumice. Within the industry, there is used the perlite, namely, the volcanic glass, which is containing up to 3-5% of the constitutional (in the bound state) water.