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Amosite Asbestos Under the Microscope

Amosite Asbestos,Phase Contrast Dispersion Staining

The D-line refractive index perpendicular to the length of this sample of amosite asbestos is about 1.677. It matches the refractive index of the Cargille High Dispersion 1.680 liquid at a wavelength of about 650 nanometers. At this wavelength the Cargille liquid has a refractive index of about 1.672, as does the amosite. This Type of Dispersion Staining produces two colors for any given wavelength match between a given liquid and solid with a fixed single linear polarizing filter. The wavelength at which the refractive index of the fiber and the medium match can be more precisely determined.

Transmitted Linear Polarized Light Perpendicular to the Fiber Long Axis, Phase Contrast Dispersion Staining


Amosite asbestos is the fibrous form of amphibole in the cummingtonite-grunerite family. Its chemical composition is (Mg, Fe, Mn)7[Si8O22](OH) 2. It is the next most common commercial asbestos after Chrysotile.

Significance in the Environment:

Amosite is a hazardous material and exposure should be very carefully limited. It is one of the more hazardous of the asbestos minerals.

Amosite asbestos was used primarily for boiler and steam pipe insulation and for sound proofing products like acoustic ceiling tile. It is not a common form of amphibole and so its presence in the environment generally indicates the disturbance of an asbestos containing construction material.

Characteristic Features:

Amosite fibers tend to be straight and are rather stiff. The fibers tend to be bundles and the terminations are often Well broomed. They show good dispersion colors when dispersion staining is used and they are mounted in a high dispersion 1.680 refractive index oil.

Associated Particles:

The two most common non-fibrous materials that amosite is associated with are magnesia and gypsum. A very common block form of insulation containing amosite was simply designated as Magnesia 80. It is 80% magnesia (magnesium oxide) and 20% asbestos. The asbestos content ranges from 20% amosite to various blends of amosite and chrysotile. The gypsum formulation was similar though often calcite (limestone) would be blended into the gypsum.

When used in acoustic ceiling tile it is generally mixed with glass fiber and an epoxy binder.


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