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The amphibole minerals from Franklin and Sterling Hill are varied and numerous, and Palache (1935) provided much morphological data. Many amphiboles occur within the surrounding Franklin Marble and the local gneisses. The nomenclature of amphiboles has undergone much evolution in the last half-century; the nomenclature used here is that of the IMA-approved system published by Leake (1978). Although limited in scope, the best extant study of amphiboles from the Franklin orebody is that of Klein and Ito (1968).
In general, most amphiboles from the ore deposit at Franklin are calcic amphiboles; actinolite and tremolite are the most common of these, and most are manganese- and zinc-bearing. Many other amphiboles are also present; tirodite, an Mn-Mg species, and the most significant of these, is relatively uncommon, perhaps because of the abundance of calcium in orebody assemblages. The amphiboles from both Franklin and Sterling Hill require much more study. Amphibolite rocks to the west of Franklin and Sterling Hill were studied by Collins (1971), with a judicious eye on their Mn and Zn contents.
Pargasite, edenite, magnesiohornblende, pargasitic hornblende, and edenitic hornblende are all present in the Franklin-Sterling Hill area. They closely occupy adjacent compositional space and can be identified as to formal species only by use of full chemical analyses. There are very few studied specimens for comparison.
For these reasons, the writer suggests ambiguous light-colored amphiboles from the marble quarries be called “pargasite;” those of light color to medium green or brown color from calcic assemblages in the orebodies be called “tremolite” or “actinolite;” and ambiguous very dark-colored amphiboles from the ore deposits be called “hornblende,” pending chemical analyses. For those amphibole specimens which lack even these general characteristics, the best name designation is the general one, amphibole. The amphiboles found in the Franklin-Sterling Hill area are listed below.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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This
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