Siderites are metallic meteorites composed mainly of iron which probably come from asteroids a few hundred kilometres in diameter which were pulverised in a collision. Siderites probably come from the iron-nickel core of these asteroids, large enough for a differentiation process to have led to a structure similar to that of the Earth with a mantle and a core.
The Widmannstätten structure is the appearance of many meteorites during a chemical test . When they are cut and then attacked by nitric acid, characteristic patterns appear due to the intermingling of the two ferrous minerals containing 6% to 16% nickel, kamacite and taenite.
This is an excellent test to know if a specimen is a true meteorite. Among the siderites, 90% are what are known as octahedrites which are the ones that react to the test in this way.