Transmitted Off Cross Polarized Light Illumination
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. The flakes often contain darker, less hydrated nuclei.
The form of the limonite particle reflects the shape of the interface between the oil and the
water layer. This flat sheet indicates a very flat, smooth interface. 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.
The quartz in this image is probably a filler or bulking agent from a polymer used in the Transformer
The quartz particle is sharply angular and shows no weathering. It is a very pure form of quartz
with no inclusion other than water. The Inclusions seen in the particle are vacuum chambers with
small drops of water that would fill the cavity with water vapor at the temperature at which the
crystal grew. This is a commercial grade of quartz and not a random natural mineral.
Significance in the Environment:
Free water is accumulating on the surface of sheet iron and is corroding the iron. Growth of crystal sites in the
limonite film indicate that this has been occuring for at least many months.
Characteristic Features:
Associated Particles:
References:
