Shock darkening
Shock darkening is the blackening of a chondrite when an impact forces tiny droplets of metal and sulfide into its silicate grains.
Shock darkening happens when a chondrite is hit hard enough for its metal and iron sulfide grains to melt. The molten droplets are injected into countless fine cracks in the surrounding silicate crystals, coating them with dark films and specks. The result is a dark grey to black rock, sometimes called a black chondrite.
Shock darkening is significant because it changes how a rock reflects light. A shock-darkened ordinary chondrite looks much darker in a telescope, more like a carbonaceous asteroid, so some dark asteroids may be shocked ordinary chondrite material. The Chelyabinsk meteorite, which fell in Russia in 2013, contained a substantial shock-darkened lithology alongside lighter material.
Shock darkening is identified on cut surfaces as dark regions in an otherwise pale rock, and in thin section by metal and sulfide veinlets within silicate grains. It usually goes with high shock stages and with shock veins and melt pockets.
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Level: Expert Advanced