Guide to Particle Identification Under the Microscope

Guide to Particle Identification

This is part of a guide to the identification of particles seen in samples of free particles. It is designed to allow access to files using any significant feature noticed by the microscopist rather than requiring a specific set of measured parameters. Often the most significant feature of a particle is unique to that particle type and so is not a useful diagnostic element for a broader Key for particles in general. This guide will lead to the same particle through a number of different paths depending on features and the order of significance placed on those features by the microscopist/analyst. When a particle is found that appears to be similar to the one being identified it may be useful to go to the file of particles of that type. For instance, if it looks like a starch grain then it may be useful to go to the "Starch" file in this gallery and see a larger variety of starch grains for comparison. The photographs of the particles shown here are both from standard sets and from environmental samples collected over many years by this laboratory.

Agglomerated Particles

Agglomerates are particle clusters that indicate specific activities or conditions. Agglomerates are very fragile and can only be recognized in tapelifts where the spatial distribution of the particles is retained during the sampling process.

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PARTICLES BY OPTICAL PROPERTIES

Transparent Anisotropic Particles

Transparent anisotropic particles are particles that are brighter than the background when crossed polarizing filters are used to view the particles.

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Isotropic Particles

These are particles that are dark in all orientations when viewed between crossed polars.

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Black (opaque) Particles

These are particles that are black with transmitted brightfield illumination but may look very different with cross-polarized transmitted light or with reflected light.

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PARTICLES BY SHAPE

Round or Spherical Particles

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Elongated Barbed Particles

These are elongated particles that have barbs along their length. They may be isotropic or anisotropic, transparent or opaque.

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Cellular Particles

Colored Particles

This file includes transparent particles of any shape that have a predominant color when viewed without polarizing filters. Clothing Fibers and paints can be any color and should be keyed out as "Fibers" or, in the case of paints, as spheres or agglomerates.