Standard Reference Material (SRM) 1866b is comprised of three commercial-grade
asbestos materials that were, or are, commonly used in commerce. These asbestos materials are typical of
the asbestos found in bulk samples during routine asbestos inspections of building materials. The optical
properties serve as a primary calibration standard in the identification of asbestos with polarized light
microscopy (PLM). A unit of SRM 1866b consists of a set of three bottles: one bottle containing chrysotile,
one bottle containing asbestiform grunerite (amosite), and one bottle containing asbestiform riebeckite
(crocidolite). Each bottle contains between 1 gram and 3 grams of material.