Glass
Glass is a solid with no crystal structure, formed when melted material cools too fast for crystals to grow.
Glass is a solid in which atoms are jumbled rather than neatly arranged. It forms when a liquid cools so quickly that crystals do not have time to grow. Window glass, volcanic obsidian and many types of impact glass are examples.
Glass is common in meteorites. The fusion crust is a thin layer of glass and tiny crystals formed as the outside melted during atmospheric entry. Many chondrules contain glass between their crystals. Shock veins and melt pockets contain glass quenched after impacts. In some lunar meteorites, beads of volcanic and impact glass are mixed into the soil.
Glass is not permanent. Over time, heat makes it crystallise, which is why primitive chondrites still have chondrule glass while more heated ones contain feldspar instead. Water also attacks glass, altering it to clay. On Earth, natural glasses such as tektites and Libyan Desert Glass record past impacts; they are not meteorites, but melted Earth rock.
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Level: Explorer Ages 10 and up