Asbestos bulk fiber identification microscopes that meet NIOSH 9002 standards include a polarized light microscope 100x - 400x with a 10x dispersion staining objective. A stereo microscope with 10x - 45x is also often used.
Dispersion staining is a process where color is imparted to colorless objects with a refractive index measured and used to identify the object being tested. Microscope World's asbestos bulk fiber identification microscopes use 10x annulus dispersion staining objective for the infinity corrected microscope. Different colors are observed when the fiber is oriented parallel or perpendicular to the polarizer direction. You can learn more about the US Center for Disease Control's NIOSH 9002 methods here.