Excluding game, the Excursion de France additionally supplies a chance to (re)uncover our landscapes and now and again their geological oddities. This Tuesday, July 14th, Excursion de France riders will pass the Cantal volcanoes with out concern of a puncture… but, they’re crossing glass mountains! Certainly, maximum volcanic lava is basically fabricated from glass.
To a geologist, communicate of “crystalline glass” is an aberration: in nature, glass is an amorphous cast – this is, disordered on an atomic scale, in contrast to crystals. It is one of those frozen liquid.
After we speak about glass, we must be cautious in regards to the polysemy of the time period: there may be glass that guy has been making for millennia to design home windows or bins, as an example, however there could also be an entire vary of herbal glasses.
As Daniel R explains. Neuville, a analysis affiliate on the Institut de Body du Globe in Paris, “glass” is man-made molten silicate, whilst volcanic lava or magma is silicate from deep throughout the earth — or from different planets.
When a lava waft cools temporarily, its subject matter can not crystallize, so it freezes within the type of glass. A “frozen edge” is seen round sure streams, veins or volcanic bombs.
Sure rocks are in particular wealthy in glass, akin to silica-rich magmas in addition to acidic magmas.
With one of these chemical composition, the molecules have a tendency to polymerize, and is the reason their prime viscosity. This consistency limits the diffusion of components, which then fail to settle in the best puts and shape crystals. Polymerization ends up in a disorganized rock (versus a crystal) that paperwork a pitcher upon cooling: obsidian.
Obsidian (Landmannalaugar, Iceland). : Patrick de Vever, 2022, Credit score Supplied (No Reuse)
There could also be impactite or tektite glass. Impactites are herbal glasses shaped all through an asteroid have an effect on. In contrast to tektites, they don’t seem to be projected into the ambience. Lines of the impacting meteorite are discovered within the chemical composition of the impactite.
The Pantasma Valley, in northern Nicaragua, is thought to were created through an asteroid have an effect on 800,000 years in the past. CNRS Business glass
Business glass is received through melting silica rock, basically sand. Components are regularly added to change its homes: Pyrex, as an example, extra immune to thermal surprise than odd glass, is enriched with boron.
The robust of this global have lengthy possessed very uncommon and subsequently valuable items. Amongst this stuff there have been additionally cups, i.e. glasses, fabricated from “mountain crystal”, i.e. quartz (crystallized silicon oxide). Those items had a powerful luminous glow and a particular sound. To mimic those valuable items and to make “crystal” glasses, lead oxide used to be added to the silicon composition, which provides it a shine and makes it conceivable to procure a function sound.
Two “crystal” items at the left: a bowl of rock crystal (quartz). Treasure MNHN DR Proper: Crystal glass. This glass (object) is actual glass (subject matter): the lower aspects permit a greater play with the L Carpentier mild. Supplied through the creator
The extra lead, the extra crystalline the sound: the rate of sunshine is determined by the medium during which it propagates. The denser the medium, the more potent the sunshine is mirrored; it may possibly even move so far as overall mirrored image if the crystal is lower into aspects, which then play the function of a reflect. For a similar explanation why, the sound that such glass produces when it vibrates is sharper, extra… crystalline.
An extended model of this newsletter used to be revealed on June 29, 2026 at the Planet Terre ENS Lyon site.
