Asbestos is a form of certain serpentine or amphibole minerals that has crystallized in a particular habit known as asbestiform. Amphibole minerals are often encountered in metamorphic geological environments, but the majority will not have crystallized in the asbestiform habit. Thus, ore deposits in these environments may include coarsely crystalline amphiboles that can produce cleavage fragments when the rocks are crushed. These fragments may meet morphological criteria that cause them to be designated as "fibers" but without their being asbestiform per se. In an attempt to distinguish cleavage fragments from asbestiform fibers, the American Society for Testing and Materials (ASTM) International Standard D7200-06(2) includes a procedure for determining whether the particles observable under the phase contrast microscope that meet a morphological definition of a fiber are likely to be asbestiform fibers or cleavage fragments. (The morphological definition of a fiber is that described in the National Institute for Occupational Safety and Health [NIOSH] 7400 "A" counting rules, i.e., >5 mu/m in length and with aspect ratio [length:width] greater than or equal to 3:1). Under ASTM D7200, any particle meeting the definition of a fiber that is curved or has any morphology that suggests that it is a bundle of fibrils is automatically assigned to a class of particles (Class 1) defined as potentially asbestiform, whatever its actual dimensions.