Iron-Oxide Concretions and Nodules, 1

Iron-oxide nodules or concretions are the most common kind of meteorwrong sent to us. Hematite and magnetite are two common iron-oxide minerals. Most iron ore deposits consist mainly of hematite, magnetite, or both. Iron-oxide concretions, iron-oxide nodules, and ironstones are often mistaken for meteorites because their unusual, frequently bizarre, shapes catch people’s attention and they are heavy.

Hematite concretions form by precipitation of iron oxide from iron rich solutions. Hematite nodules are often formed in sedimentary rocks like limestone by oxidation of pyrite or marcasite (iron sulfide) crystals. Concretions and nodules, which may also be composed in part of the iron oxy-hydroxides, limonite and goethite, come in a wide variety of shapes. Sometimes they’re shiny on the surface, which might give the impression of a meteorite fusion crust. Note that while pure hematite is rich in iron, it does not attract a simple magnet. Magnetite, on the other hand, is highly attracted to magnet, and it often forms nodules, too. In rocks highly rich in magnetite-hematite nodules, some parts of the the rock may attract a magnet and other parts may not.

Hematite is easy to identify because it makes a red streak. Also, hematite concretions are denser (heavier for their size) than any kind of stony meteorite or most other kinds of Earth rocks. For example, the specific gravity of an ordinary chondrite (the most common kind of meteorite) is about 3.9 whereas the specific gravity of a hematite concretion is 4.2-5. Magnetite (often blackish) is even denser with a specific gravity up to 7.9

Nearly all the following photos here were sent to me by the people who found the rocks. Iron oxide concretions are dark, and in the process of “improving” some of these photos, I may have changed the color. Not all of these rocks are, technically, concretion or nodules, but all are rich in iron-oxide minerals.

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri

Missouri – The one on the left has a botryoidal texture

Missouri

Somewhere in the U.S.

Somewhere in the U.S.

Somewhere in the U.S.

Texas

Texas

All from somewhere in the U.S.

U.S.

Brazil