What is a glass in geology ?
Glass : definition
Although some glasses are considered as minerals or rocks (case of obsidians), they do not have an ordered atomic structure nor most of the time a defined chemical composition. They generally result from thermal shocks (sudden cooling of a magma or a fluid in contact with water). Volcanic rocks, cooled rather brutally in general, frequently admit a certain proportion of glass.
Glass, a material so common and seemingly so simple, remains a complex body which partially escapes our Cartesian logic because it does not have a unanimously accepted definition. One of the most classic consists in considering glass, or rather glasses, as solids obtained by congealing a liquid which has not crystallized.
The most common glasses are silica glasses, obtained by melting extra-siliceous sand (over 97% SiO2) to which various fluxes and additives have been added.
Glass, a material so common and seemingly so simple, remains a complex body which partially escapes our Cartesian logic because it does not have a unanimously accepted definition. One of the most classic consists in considering glass, or rather glasses, as solids obtained by congealing a liquid which has not crystallized.
The most common glasses are silica glasses, obtained by melting extra-siliceous sand (over 97% SiO2) to which various fluxes and additives have been added.
Moldavite : meteoritic glass
Snowflakes obsidian from USA
Lybian desert glass from Egypt