From Halopedia, the Halo wiki
Lechatelierite is a type of silica glass. It is an amorphous form of silicon dioxide (SiO2), lacking any crystalline structure, and is thus a mineraloid rather than a true mineral, although it is sometimes grouped with quartz.
Lechatelierite can be formed in a number of ways. One of the most common ways that this occurs naturally is through the high-temperature melting of sand during a lightning strike; this produces a specific from of lechatelierite called "fulgurite" which is often hollow, irregular, and tubular. Lechatelierite can also be formed through the shock metamorphosis of sand or even silica-rich rocks, such as sandstone or granite, by the high pressure of meteorite impact cratering, and is thus a common component of ejecta. This form of lechatelierite is especially prevalent in the Libyan Desert on Earth. Lechatelierite can even be formed by the detonation of nuclear weapons, a phenomenon first observed following the Trinity nuclear test in 1945.
Lechatelierite is a common product of the Covenant tactic of glassing, the orbital plasma bombardment of a world to render it uninhabitable. An observer offered this description: "The so-called glass is a mineral called lechatelierite. It is a result of the Covenant lances striking the surface of the planet with plasma, converting the topsoil to glass. Any attempt to make a glassed planet habitable would mean cutting the surface down to below the topsoil."
The Shard Chamber on High Charity contained many slabs of lechatelierite from glassed worlds. The Hierarchs would often meet their Fleetmasters there. Fleetmasters brought their own slabs of lechatelierite to present to the hierarchs when meeting there, from any worlds they had purged since their last meeting there.
During the Human-Covenant War, the Covenant Empire glassed scores of human colonies, leaving their surfaces desolate and covered in lechatelierite. Such worlds, called "the glasslands", were uninhabitable without extensive terraforming. Some, such as Meridian, were sparsely covered such that they could be rehabilitated within twenty years, although others were so severely affected that terraforming efforts were projected to take upwards of a century.
By 2558, the BXR Mining Corporation was involved in the commercial mining and sale of lechatelierite extracted from glassed worlds, such as Bliss. Such mined lechatelierite was sold in the inner colonies and converted into commodities such as housing insulation. Lechatelierite that was "organically enriched", containing carbon impurities that were the remnants of the plant, animal, and even human life of the former colonies, was especially valuable due to the zeolites it contained.
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