A fusion crust is the most characteristic feature that distinguishes a meteorite from a plain old Earth rock. If a rock does not have a fusion crust and does not contain iron-nickel metal, then there is no reason to suspect that it is a meteorite, regardless of what other meteorite-like features it may have.
This is one of many stones of the Gao-Guenie (H5 chondrite) meteorite that fell in Burkina Faso (western Africa) in 1960. The stone has a nearly complete fusion crust. Such stones are always rounded, with no sharp edges of corners. There is a hint of a regmaglypt on the far right. Photo credit: Randy KorotevNot all fusion crusts are glassy smooth; I have seen a number of meteorites having fusion crusts with this distinctive texture. Photo credit: unknown correspondentThis is a freshly fallen stone of the Katol (L6 chondrite) meteorite found in India on May 22, 2012, after a meteor shower. Note the regmaglypts and the light-colored interior on the left where the fusion crust has chipped off.The Ash Creek (L6 chondrite) meteorite was an observed fall in Texas on February 15, 2009. The meteor was captured on video, where it is seen to break apart. Hundreds of small stones have been found around the town of West. Here are 11 of them from the collection of Karl Aston. The stone in the lower left is the most rounded. It has a complete fusion crust and some regmaglypts. Among these stones, it is probably the earliest to have broken off the main mass of the original meteoroid. Several other stones have complete or nearly complete fusion crusts, regmaglypts, and edges rounded by ablation. These stones probably broke from the main mass lower in the atmosphere. The large stone in the middle has a smooth, dark fusion crust on the bottom side that we cannot see, but on top there is a light fusion crust and only a little ablation. This break must have happened at even lower altitude, but still high enough that heating occurred. Finally, some stones have breaks and chips that happened low in the atmosphere or upon hitting the earth. The light-colored interior is visible on these stones. Thanks to Karl Aston for loan of the stones. Photo credit: Randy KorotevThis is one of the many Park Forest (L5 chondrite) stones that fell in Chicago on March 26, 2003. This one went through a roof and broke into four pieces. Many Park Forest stones have a patchy fusion crust. The meteorite is a breccia, with light gray clasts in a dark matrix. Photo credit: Carrie Seniw
Here are photos of a meteorite named Saint-Pierre-le-Viger (L5-6 chondrite) that fell in France on February 13, 2023. The first piece was found 2 days later. Note: There is no crater or hole in the ground.
I was sent these photos by someone in Morocco claiming that they are photos of 2 of the 35 pieces of meteorite NWA 7325 (achondrite-ung). Maybe they are, maybe they are not, but they are good photos of fusion crust. The stones are about 2-3 cm in size.This is another photo sent to me by someone in Moroccoof a broken meteorite. The unnamed meteorite is a bit weathered. The fusion crust has lost its gloss. You cannot see the metal from this distance but you can see red spots where it has rusted.Fusion crusts on feldspathic lunar meteorites are lighter colored than those on other kinds of meteorites mainly because they contain less iron. These lunar meteorites contain 2.1-4.5% Fe (iron) whereas chondrites contain 18-29% Fe.
A fusion crust is the most characteristic feature that distinguishes a meteorite from a plain old Earth rock. If a rock does not have a fusion crust and does not contain iron-nickel metal, then there is no reason to suspect that it is a meteorite, regardless of what other meteorite-like features it may have.
