Etching of a polished surface with a mixture of nitric acid in alcohol reveals a structure that is shown only by meteoritic iron and which is difficult to produce artificially. Iron meteorite from Chinautla, Guatemala, found 1902. Polished and etched surface, with the characteristic structure. They are mainly composed of olivine and a pyroxene mineral virtually absent in terrestrial rocks. The minerals form millimeter-sized, nearly spherical particles of different internal structure called chondrules.
Most stony meteorites contain chondrules and therefore are called chondrites.
Chondrites have not been melted since their formation and are composed of almost the same proportion of elements as the Earth. They are believed to represent the materials the Earth formed from. The most primitive of all meteorites are the carbonaceous chondrites. Small amounts of organic compounds which formed in space without involvement of life are present in these meteorites. The achondrites are stony meteorites without chondrules.