metal, iron, & nickel

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About 95% of all meteorites contain iron-nickel (FeNi) metal. "Iron-nickel" means that the metal is mostly iron but it contains 4-30% nickel as well as a few tenths of a percent cobalt. Iron-nickel metal in meteorites also has high concentrations (by terrestrial standards) of rare metals like gold, platinum, and iridium. It's usually easiest and cheapest to test for nickel, however, because it's more abundant than the rare metals.

Metal grains reflecting light in a polished slice of the ordinary chondrite Faucett (H5). Click on image for enlargement.
Photo by Randy Korotev.

Most metal-bearing meteorites are stony meteorites known as ordinary chondrites; the rest are irons and stony irons. Among ordinary chondrites, the most common type, H-group chondrites (45% of all meteorites), have the most metal, 15-20% by mass. L-group chondrites (40% of all meteorites) have some metal, 7-11%. LL-group chondrites (15% of all meteorites) have the least metal among ordinary chondrites, 3-5%. Because chondrites are rich in metal and the metal is rich in nickel, all chondrites have a bulk (whole rock) concentrations of Ni (nickel) of 1.0-1.8% (i.e., 10000-18000 ppm). That's 100-1000 times greater than practically any terrestrial (Earth) rock. An Earth rock with as much as 1.0-1.8% Ni would be a nickel ore.

Notice (left) that metal grains are typically less than a millimeter in size.

Metal grains reflecting light in a sawn slice of the Taffassasset (CR-anom or achondrite). Click on image for enlargement. Note in the enlargement on the right the saw marks in the metal grains. This is a good way to distinguish metal from shiny sulfide minerals like pyrite - the sulfides grains won't look so severely scraped. Photo by Randy Korotev.

Sawn, polished, and etched slab of the Campo del Cielo (IAB) iron meteorite. Notice the rusty spots. Click on image for enlargement. Photo by Randy Korotev.

Sawn, polished, and etched slab of the Gibeon (IVA) iron meteorite. This meteorite has a distinct Widmanstätten pattern. Click on image for enlargement. Photo by Randy Korotev.

Try This

Sometimes it's hard to tell the difference between metal and shiny nonmetals like some sulfide and oxide minerals. One easy test for grains or slabs that are at least a few millimeters in size is simply to measure the electrical resistance with an ohmmeter. You can buy handheld multimeters in any good hardware store for $30, and they're great for checking the voltage on partially used batteries. In resistance mode (ohms), putting the leads some distance apart on any of these iron meteorites would give a low resistance - <100 or probably <10 ohms. (This won't work on an ordinary chondrite because the iron grains aren't connected.) A shiny hematite or pyrite aggregate will have very high electrical resistance because they do not conduct electricity.

Sawn and polished slab of the metal portion of the Glorieta Mountain (ung) pallasite. Photo by Randy Korotev (natural light).

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Prepared by:

Randy L. Korotev

Department of Earth and Planetary Sciences
Washington University in St. Louis

Please don't contact me about the meteorite you think you’ve found until you read this and this.