Amphibole Asbestos Mineralogy

Amphiboles are common silicate minerals found in many types of rocks. Although most occurrences of amphibole are non-asbestiform, large deposits of some asbestiform amphiboles have been exploited commercially, particularly from deposits in South Africa, Australia, and Finland. Those that have been exploited commercially typically belong to a small subset of amphibole mineral species (riebeckite or crocidolite, grunerite, anthophyllite, actinolite, and tremolite). As discussed below, other amphiboles may also occur with asbestiform habits, including winchite and richterite, which are associated with human exposures in Libby, Montana. In addition, some amphiboles occur with fibrous but non-asbestiform habits, such as byssolite (the stiff-fibered form of actinolite).

Amphibole minerals form a family of double-chain silicates, which are composed of I-beams, as shown in Figure 3.2. Chains of polymerized silica tetrahedra are on both the top and bottom of the I-beam. Between the

FIGURE 3.2 Amphibole structure. a) Individual I-beam down a-axis, showing two chains of polymerized silica tetrahedra (one darker) overlying strip of metal octahedra (shown as ball-and-stick). A sites are in channels formed by stacked I-beams; B sites appear as larger dark atoms at edges of the octahedral strip; C sites appear as smaller black atoms in middle of octahedral strip; T sites appear as triangles. Larger white atoms are oxygen atoms or hydroxyl groups. b) Individual I-beam down the c-axis, showing two tetrahedral chains on top and bottom of I-beam. c) Amphibole structure down c-axis, showing interconnectivity of I-beams, various cation sites, and common cleavage planes in amphibole that would lead to surfaces found in non-asbestiform amphibole particles. SOURCE: Papike et al. (1969)

FIGURE 3.2 Amphibole structure. a) Individual I-beam down a-axis, showing two chains of polymerized silica tetrahedra (one darker) overlying strip of metal octahedra (shown as ball-and-stick). A sites are in channels formed by stacked I-beams; B sites appear as larger dark atoms at edges of the octahedral strip; C sites appear as smaller black atoms in middle of octahedral strip; T sites appear as triangles. Larger white atoms are oxygen atoms or hydroxyl groups. b) Individual I-beam down the c-axis, showing two tetrahedral chains on top and bottom of I-beam. c) Amphibole structure down c-axis, showing interconnectivity of I-beams, various cation sites, and common cleavage planes in amphibole that would lead to surfaces found in non-asbestiform amphibole particles. SOURCE: Papike et al. (1969)

TABLE 3.2 Mineral Names, Varietal Names, and Atomic Site Compositions^ for Amphiboles That Have Been Commonly Encountered in an Asbestiform Habit

Mineral (variety)

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