El Medaño is a very rare type of stone meteorite known as a brachinite. Most stone meteorites originated on asteroids and most are part of the large group known as chondrites. Chondrites are named after the chondrules (small, glassy spheres) that they contain.
Much more scarce than chondrites are the achondrites — stone meteorites without chondrules — and brachinites are part of this group. Brachinites take their name from the Brachina meteorite found in 1974 in Brachina, Australia. Only about 1 out of every 1,300 recovered meteorites is a brachinite, making them one of the rarest types known to science. Brachinites are mostly made up of the mineral olivine which, in its pure gemstone form, is known as peridot. That gives the greenish hue which can be seen in specimens, like this one, that have been sliced and polished in the laboratory.
Only one 2,228 gram piece of El Medano was recovered near the top of a large hill from the desert pavement by Steve Arnold of Meteorite Men in November 2018 on a Meteorite Adventures meteorite hunting expedition in the El Médano region of the Atacama Desert.