Asbestos Fibers and Other Elongate Mineral Particles: State of the ...

Table 1. Definitions of general mineralogical terms (Continued)
142
Glossary of Geology, 5th ed.
[American Geological
Institute 2005] Leake et al. [1997] NIOSH [1990a]
Dictionary of Mining,
Mineral, and Related
Terms [U.S. Bureau
of Mines 1996]
[Note: Footnotes identify the Primary
Source Citation for the definition]
Term
Each of the six commercially exploited
asbestiform minerals also occurs in a
nonasbestiform mineral habit. These
minerals have the same chemical
formula as the asbestiform variety, but
they have crystal habits where growth
proceeds in two or three dimensions
instead of one dimension. When
milled, these minerals do not break
into fibrils but rather into fragments
resulting from cleavage along the two
or three growth planes. Particles thus
formed are referred to as cleavage
fragments and can meet the definition
of a fiber for regulatory purposes.
Nonasbestiform
habit
[crystal] A crystal form having three, four,
six, eight, or twelve faces, with parallel
intersection edges, and which is open
only at the two ends of the axis parallel
to the intersection edges of the faces.
Prism 1. An open crystal form with
faces and their intersecting
edges parallel to the principle
crystallographic axis. Prisms
have three (trigonal), four
(tetragonal), six (ditrigonal
or hexagonal), eight
(ditetragonal), or twelve
(dihexagonal) faces. The ninesided
prisms of tourmaline
are a combination of trigonal
and hexagonal prisms.
See footnotes at end of table. (Continued)
NIOSH CIB 62 • Asbestos