PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 2 DECEMBER 15, 1916 Number 12 
THE ORIGIN OF VEINS OF THE ASBESTIFORM MINERALS 
By Stephen Taber 
DEPARTMENT OF GEOLOGY. UNIVERSITY OF SOUTH CAROLINA 
Received by the Academy, November 4, 1916 
In its strict application the name asbestos is limited to the fibrous 
varieties of the monoclinic amphiboles. The term is commonly ap- 
plied, however, to those minerals having a highly developed fibrous (as- 
bestiform) structure. When such minerals occur in veins the fibers are 
parallel, and run transverse to the strike of the veins. Hence they 
have been called cross-fiber veins. 
Microscopic examination shows that bundles consisting of thousands 
of fibers of chrysotile or amphibole asbestos behave as crystal units, an 
entire bundle exhibiting the same optical properties as any one of the 
component fibers. All asbestiform minerals have prismatic cleavage, 
and this suggests that the fibrous structure may be due to an abnormal 
development of the cleavage, or at least that the separation of the 
fibers takes place largely along cleavage planes. The highly fibrous 
structure of the asbestiform minerals is not, however, a crystallization 
phenomenon in the sense that it is due solely to the inherent physical 
properties of the crystal molecule, for all minerals having asbestiform 
varieties occur in non-fibrous as well as fibrous forms. 
A comparative study of the occurrence of all commonly fibrous min- 
erals indicates that the peculiar structure of asbestiform minerals is due 
to the accentuation of a normal prismatic habit and cleavage by phys- 
ical conditions which have limited crystal growth to a direction paral- 
lel to the principal axis. Many minerals possessing perfect prismatic 
cleavage do not have fibrous varieties, but they are always minerals that 
crystalHze from fusion or solution under conditions permitting of growth 
in more than a single direction. All asbestiform minerals are second- 
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