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Anthophyllite

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The name anthophyllite comes from the Latin word anthophyllum, which means “clove”—a reference to the mineral’s clove-brown to dark brown color. Specimens can also be pale green, gray, or white. Anthophyllite is usually found in columnar to fibrous masses. Single crystals are uncommon; when found, they are prismatic and usually unterminated. The iron and magnesium content in anthophyllite is variable. The mineral is called ferroanthophyllite when it is iron-rich, sodium-anthophyllite when sodium is present, and magnesioanthophyllite when magnesium is dominant. Titanium and manganese may also be present in the anthophyllite structure. Anthophyllite forms by the regional metamorphism of iron- and magnesium-rich rocks, especially silica-poor igneous rocks. It is an important component of some gneisses and crystalline schists and is found worldwide. Anthophyllite is one of several minerals referred to as asbestos.

Name: From the Latin anthophyllum, meaning clove, in allusion to the mineral’s color.

Association: Cordierite, talc, chlorite, sillimanite, mica, olivine, \hornblende,” gedrite, magnesio-cummingtonite, garnet, staurolite, plagioclase.

Polymorphism & Series: Forms a series with magnesio-anthophyllite and ferro-anthophyllite.

 Mineral Group: Amphibole (Fe{Mn{Mg) group: 0.1 Mg=(Mg + Fe 2+) 0.89; (Ca + Na)B < 1.34; Li < 1.0; Si ¸ 7.0.

Chemical Properties of Anthophyllite

Chemical Classification Inosilicates
Chemical Composition (Mg,Fe)7Si8O22(OH)2

Physical Properties of Anthophyllite

Color White, greenish grey, green, clove brown, or brownish gree
Streak White to greyish-white.
Luster Vitreous, Pearly
Cleavage Perfect Perfect on {210}, imperfect on {010}, {100}
Diaphaneity Transparent, Translucent
Mohs Hardness 5½ – 6 on Mohs scale
Tenacity Brittle; elastic when fibrous
Diagnostic Properties Characterized by clove brown color, but unless in crystals, difficult to distinguish from other amphiboles without optical and/or X-ray tests
Crystal System Orthorhombic
Fracture Conchoidal
Density 2.85 – 3.57 g/cm3 (Measured)    3.67 g/cm3 (Calculated)

Optical Properties of Anthophyllite

Anthophyllite in thin section 
Optic Sign Biaxial (+)
Birefringence δ = 0.017 – 0.023
Relief Moderate
2V: Measured: 57° to 90°, Calculated: 82° to 90°
Dispersion r > v or r < v

Occurrence

From medium- or high-grade metamorphism, in amphibolites, gneisses, metaquartzites, iron formations, granulites, and schists derived from argillaceous sediments, ultrama¯c, or ma¯c igneous rocks; a retrograde reaction product.

Distribution

From Kongsberg and Snarum, Norway. At Schneeberg, Saxony, Germany. From Norberg, Sweden. At He·rmanov, Czech Republic. In Greenland, from Fisken½sset. In the USA, from Chester¯eld, Hampshire Co., Massachusetts; the Carleton talc mine, near Chester, Windsor Co., Vermont; near Media, Delaware Co., Pennsylvania; the Day Book deposit, near Spruce Pine, Mitchell Co., North Carolina; in California, at the Winchester quarry, Riverside Co., and near Co®ee Creek, Carrville, Trinity Co.; in the Copper Queen mine, Prairie Divide, Park Co., Colorado. From Munglinup, Western Australia.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.

Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].

Mindat.org. (2019). Anthophyllite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].

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