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a group of widely distributed rock-forming crystals consisting of oxysilicate compounds of magnesium, iron, calcium, less often aluminum, and alkalies; the crystals contain water, fluorine, and sometimes chlorine. Amphiboles are components of many igneous and metamorphic mountain rocks (hornblende gabbro, diorite, amphibolite, and others) and occasionally are the only constituent (hornblendite, amphibolitic shales). The amphiboles are classified as a group on the basis of their crystallographic properties. Amphiboles crystallize in monoclinic and rhombic systems, forming prismatic crystals. The basis of the crystalline structure of amphiboles, as in the case of all silicates, is oxysilicate tetrahedrons interconnected by two or three common oxygen ions into a continuous band (see Figure 1). The basic grouping has the composition [Si4O11]; the presence of (OH)2, fluorine, or chlorine is required for every such radical in the structure. The color of amphiboles depends on their iron content; it may vary from colorless through green to black. The hardness of these minerals on the mineralogical scale is 5–6, and their density is from 2,800 to 3,460 kg/m3.

Figure 1. Crystalline structure of amphiboles

With regard to symmetry and chemical composition, the amphiboles are divided into a number of mineral groups comprising a large number of varieties which arise from wide isomorphic miscibility. Among magnesium-iron amphiboles are distinguished two varieties, rhombic (the anthophyllite-gedrite group) and monoclinic (the cummingtonite-grünerite group). Amphiboles of these two groups are encountered relatively rarely and only in metamorphic rocks. Calcium-containing amphiboles are known in monoclinic varieties. Among them are distinguished the actinolite group of alumina-free amphiboles found in metamorphic rocks, and a very large group of aluminocalcium amphiboles—the hornblendes, which are found both in magmatic and metamorphic rocks. Specific varieties are basaltic hornblende, found in effusive rocks, and alkaline hornblendes, usually part of alkali rocks. Alkaline sodium amphiboles are monoclinic (glaucophane, riebeckite, arfvedsonite, and others) and are characteristic of many metamorphic rocks and metasomatic formations. Upon deterioration or weathering, amphiboles are converted into chlorites, epidote, montmorillonitic clayey products, carbonates, hydrous ferric oxides, and silica. Fine-fibered varieties of amphiboles, known as amphibolitic asbestos, are widely used because of their chemical and thermal stability.


Betekhtin, A. G. Kurs mineralogii, 2nd ed. Moscow, 1956.
Bragg, W. L., and G. Claringbull. Kristallicheskaia struktura mineralov. Moscow, 1967. (Translated from English.)


References in periodicals archive ?
The dioritic to granodioritic and most of the granodioritic to monzogranitic plutons form linear trends on chemical variation diagrams, suggesting that magma evolution was dominated by plagioclase and amphibole fractionation.
2000 vv e know that a caldera resurgence that began during the SEE with conduit opening and alkaline trachytic to rhyolitic magma emission near the caldera margins, initial volcanism was not explosive in nature: magma could reach the surface after complete volatile release through conduit permeable walls, promoting anorthoclase and sanidine nucleation rate increment and amphibole and mica stability reduction, which generated corrosion and opatization borders in mafics.
Our findings detract from the amphibole hypothesis, whose proponents argue that the carcinogenicity of chrysotiie is due to contamination by amphiboles (Mossman ct al.
There are two main families of asbestos: amphiboles (tremolite, actinolite, crocidolite) and serpentines (chrysorile, antigorite, lizard-ite).
A representative suite of samples from mafic intrusions on Campobello Island was collected for scanning electron microprobe (SEM) analyses to quantify our petrographic analysis of amphibole, pyroxene, and plagioclase (Table I).
Clinopyroxene (diopside) occurs as scarce, ragged cores within amphibole and rarely coexists with orthopyroxene.
Although both crocidolite and Libby are amphiboles, their distinct physicochemical properties may influence the types of damage they produce.
Case-report and case-control studies showed that the lungs of mesothelioma patients contained only chrysotile fibers rather than amphiboles (Langer and McCaughey 1982; Rogers et al.
A survey on lung fiber burden in a series of consecutive necropsies supports the hypothesis that important pollution from amphiboles was present in Casale (Magnani et al.
Geological Survey has characterized the respirable fraction of asbestiform amphiboles contaminating the Libby vermiculite as approximately 84% winchite, 11% richterite, and 6% tremolite (Meeker et al.
The Phase Relationship of Talc and Amphiboles in a Fibrous Talc Sample.