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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 ?
Potency differences between chrysotile and amphiboles have received much attention in risk assessments for asbestos and may explain heterogeneity in exposure-response estimates between studies (Berman and Crump 2008a; Hodgson and Darnton 2000; Mossman et al.
This distribution of helium isotopes in the Archaean section is typical of not only the main rock varieties--gneiss and amphibolite but also of monomineral fractions of rock forming amphibole and quartz from veins and pegmatite (Fig.
32) It emerged that amphiboles are far more potent in the induction of asbestosis, lung cancer, and malignant mesothelioma than chrysotile.
Seven unaltered and fresh samples each of quartz schist and amphibole schist were analyzed for both major oxide and trace element concentrations at the Activation Laboratories, Canada, using the inductively coupled plasma analytical technique.
Commonly, nearly all the amphibole is blue green and the accompanying plagioclase compositions range from oligoclase to andesine.
The second interesting result is the difference in risk between serpentines and amphiboles.
The EMPA data of amphiboles used for the radiometry proved a scattered composition and zoned structure of these minerals in the granites studied as shown in Table 4.
Therefore, this mechanism is considered as not relevant for the Zanbil amphiboles but it is slightly true for plagioclase coarse grains (Fig.
Nomenclature of amphiboles: Report of the subcommittee on amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names.
EPA 2014c), was the site of a former mine that produced vermiculite contaminated with a mixture of asbestiform amphiboles, including winchite, richterite, and tremolite asbestos (Meeker et al.