Mineralization and magnetization of chiton teeth: paleomagnetic,sedimentologic, and biologic implications of organic magnetite

Magnetite precipitation and tooth formation in chitons (Polyplacophora) proceeds through a biochemically-controlled reduction of the mineral ferrihydrite. Resulting crystals of single-domain magnetite are closely packed against one another and are typically near 0.1 μm in diameter. The natural magnetization of these teeth is characterized by abnormally low stability to alternating field demagnetization (m.d.f. near 12 mT) but has no appreciable decay due to low-temperature cycling. Chitons may be responsible for natural magnetizations on the order of 10^?6 G in marine sediments, whereas mud bacteria could produce remanence near 10^?8 G in both marine and freshwater sediments.