Amphibole Occurrence and Uses

Occurrence. Amphibole is an important and widely distributed rock-making mineral, occurring both in igneous and metamorphic rocks, being particularly characteristic, however, of the latter. The fact that amphibole frequently contains hydroxyl and fluorine indicates that, in some degree, it is often of pneumatolytic origin Tremolite is most frequently found in impure, crystalline, dolomitic limestones, where it has been formed during the crystallization of the rock, while undergoing metamorphism. Actinolite commonly occurs in the crystalline schists, being often the chief constituent of green-colored hornblende schists and greenstones. Frequently the amphibole of such rocks has had its origin in the pyroxene contained in the igneous rock from which the metamorphic type has been derived. Cornmon hornblende is found in igneous rocks, such as granites, syenites, diorites, gabbros, and in some peridotites; it rarely occurs in the dark traps and basalts. It also occurs in the metamorphic rocks, such as gneisses and hornblende schists.

Notable localities for the occurrence of crystals are: tremolite from Campolungo, Ticino; in. the Tyrol; in Piedmont, Italy; from Russell, Gouverneur, Amity, Pierrepont, Dekalb, etc., New York; actinolite from Greiner, Zillerthal, Tyrol; hornblende from Bilin, Bohemia; Monte Somma, Italy. Actinolite frequently comes fibrous, and is the material to which the name as bestos was originally given. Has been found in the metamorphic rocks in various states along the Appalachian Mountains. Nephrite is a tough, compact variety of actinolite which supplies much of the material known as jade (see also under jadeite). A famous locality for its occurrence is in the Kuen Lun Mountains, on the southern border of Turkistan.

Names. Tremolite is derived from the Tremola Valley near Sto Gothard. Actinolite comes iron two Greek words meaning a ray and stone, in allusion to its frequently somewhat radiated structure.

Uses. The fibrous variety is used to some extent as asbestos material. The fibrous variety of serpentine furnishes more and usually a better grade oí asbestos. The compact variety, nephrite, is used largely for ornamental material by oriental peoples and is called jade.

Among the other rarer monoclinic members of( the Amphibole Group are glaucophane, NaAl(Si0₃)h.(Fe,Mg)Si0₃; riebeckite, 2NaFe(SiO.)2.FeSiO.; crocidolite, NaFe(Si03)2.FeSi0₃;arfvedson,Na₈(Ca,Mg)₃.(Fe,Mn)₁₄(AI,Fe)₂₁Si₂₁

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