Other Chain Aluminosilicates that Form Fibers

OTHER CHAIN ALUMINOSILICATES THAT FORM FIBERS 

In addition to the asbestos varieties many other examples of silicate and aluminosilicate minerals occur in fibrous form. In the following section we present data for a few selected species, indicating the types of chemical 

The pyroxenes are chemically complex but common rock-forming minerals. They resemble the amphiboles in many ways, but are actually single-chain silicates. The tetrahedral basic unit of the pyroxenes, [(Al,Si)20g] , was schematically depicted in Fig. 2.1C. The general formula for the group is Ai (B, C)i+ TjOfi, where A = Ca Fe Li+, Mg , Na- B = Mg , Fe Mn Sc+ C = Fe A Cr Ti and T = Si Al+l Within the group are several mineral series and several species that often occur in acicular or fibrous forms. One species that occurs in fibrous form is jadeite, [Na(Al,Fe )Si206], a relatively familiar name because of the popularity of this material with Oriental sculptors. 

The pyroxene group of minerals, where cations substitute one for another at interchain sites, also have a tetrahedral Si site that may contain Al. Some of these substitutions, especially those at M2, can distort the ideal crystal structures, as is depicted in Fig. 2.10. The small distortions are detected as variations in bond lengths between adjacent atoms during crystal structure analyses. These data, combined with accurate composition analyses, could indicate some of the conditions present during growth of the crystal and contribute to our understanding of why some mineral species have formed as fibers. Unfortunately, few detailed crystal structural analyses have been performed on pyroxene minerals with fibrous habits. 

As might be anticipated for minerals with chain structures, pyroxenes commonly occur in columnar, prismatic, rodlike, and acicular forms. Enstatite has been found in the form of rosettes of fine-fibrous crystals. Special names such as victorite, chladnite, and shepardite were assigned to different occurrences in this distinctive morphology, possibly because the fibrous aggregates were located in iron meteorites. However, the composition and crystal 

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OTHER CHAIN ALUMINOSILICATES THAT FORM FIBERS... 

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