Iron-nickel is technically a group of scientifically classified minerals. Most mineral collectors do not make a distinction between the individually-named minerals in this group, and refer to specimens as Iron or Iron-Nickel. Most Iron-nickel is of extraterrestrial origin, in the form of meteorites. Hundreds of meteors fall toward earth every day, but most of them burn up in the atmosphere. The few that make it to earth usually land in water, and the few that land on the ground are generally small. Meteorites usually contain a crust, which forms when they are partially molten (from the heat generated by their speed) in the atmosphere, and solidify when they cool down by landing on earth.

There are some natural deposits of terrestrial Iron-nickel, but they are rare and limited. Crystals are uncommon, although some meteorites show etched crystals on polished faces, known as widmanstatten patterns. Iron-nickel (terrestrial or extraterrestrial) develops a coating of rust if washed or if kept in a humid area. If a specimen must be washed with water, it should be thoroughly dried.

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