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Photographic gallery.  Thousands of particles under the microscope.
Rust Through the Microscope

Iron Corrosion From Oil In Transformer

The orange particle is limonite.

Transmitted Off Crossed Circular Polarized Light

Definition/Function:

Limonite is FeO-OH-nH2O. It varies in color from very pale yellow to orange-brown, depending on the amount of water in the matrix. In oil filled systems the form of the limonite particle reflects the shape of the interface between the oil and the water layer. Limonite is amorphous or cryptocrystalline but as it looses more water the nuclei convert to a more evident crystal structure. There are at least five forms of FeO-OH that have distinctive crystal structures. They include lepidocrocite, goethite, and others.

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