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Ca2(Al,Fe3+)3(Si2O7)(SiO4)(O,OH)2
Monoclinic
Epidote, a calcium iron aluminum silicate hydroxide mineral, is relatively rare at Franklin. Nuttall (1822) reported it as a laminated green mineral with garnet, and Palache (1935) reported it from the contacts of the ore and calcium silicate units. It is invariably greenish and occurs in 1-7 mm prismatic crystals, but has not been much studied.
Few assemblages have provided decent specimens or crystals. One such occurrence consists of blackish-green hedenbergite, calcite, pyrite, andradite, ferroaxinite, and fluorapophyllite from the Palmer Shaft at Franklin, and is described under fluorapophyllite (Betancourt, 1989). A second notable, but sparse occurrence is of superb greenish-brown, euhedral 2-5 mm crystals, in sprays associated with franklinite, rhodonite, willemite, and johannsenite, and discussed herein with the johannsenite which occurs epitactic on rhodonite from Franklin. An analysis of these latter crystals is presented in Table 7, showing minimal substitution of Mn and Zn and a composition approximating that of end-member epidote, with Al:Fe = 2:1. Specimens of epidote replacing scapolite are in some museum collections, but their source is ambiguous. Microcline is commonly associated.
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| Table 7. Chemical analyses of epidote and vesuvianite. | ||
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At Sterling Hill, epidote was found as 4-5 mm crystals associated with stilbite and manganaxinite on the 1300 level, and it is locally associated with tennantite, actinolite, erythrite, and other minerals in various parts of the mine. An occurrence in a veinlet assemblage in wollastonite-bearing rocks was described by Jenkins (1994).
Epidote is very common in the mines at Balls Hill, especially the Gooseberry Mine, where it occurs in 10-cm masses associated with andradite, magnetite, and hedenbergite.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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This
page created: January 11, 2001 |
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