Widmannstätten

The Widmannstätten structure is the appearance, during a chemical test, that certain meteorites very rich in iron called siderites take. When they are cut and then attacked using nitric acid, characteristic patterns appear due to the intermingling of the two ferrous minerals containing 6% to 16% nickel, kamacite and taenite.

(Credit: NASA)

This is an excellent test to know if the specimen is a true meteorite. Among the siderites, 90% are what are known as octahedrites and these are the ones that react to the test in this way.