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NaCa2(Fe,Mg)5Al2Si6O22(OH)2
Monoclinic
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| Figure 17-38. Crystal drawings of hastingsite from Sterling Hill. These are two projections of the same crystal. Drawings are from Palache (1935) who provided crystallographic data. | ||
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Hastingsite, a sodium calcium iron aluminum silicate hydroxide mineral of the amphibole group, was first reported from Sterling Hill by Credner (1866) and from Franklin by Kloos (1886); additional data was provided by Palache (1935). The name gamsigradite was applied to this material at one time.
Local hastingsite has been little studied. The analysis of Kloos (1886) provided by Palache (1935) is calculated as a magnesian hastingsite using the nomenclature of Leake (1978). The writer has analyzed material which fits the description of Kloos (1886), and which is labeled as coming from Franklin, and found the composition to be similar to that reported by Kloos. The writer also analyzed the lustrous black 1-2 mm crystals which occur epitactic on Sterling Hill augite (formerly called jeffersonite), and found them to be magnesian hastingsite; the analysis is given in Table 12.
Hastingsite was described by Reilly (1983) (using the old name ferrohastingsite) from Sterling Hill, in drill hole #124, 111 feet from its origin on the 340 level. It was found as an alteration product of diopside in an assemblage of calcite, franklinite, diopside and grossular. Four microprobe analyses were provided; the most iron-rich of these yielded SiO2 35.02, Al2O3 12.51, CaO 10.74, FeO 27.31, MnO 0.35, MgO 2.79, K2O 3.50, ZnO 1.63, ClO (sic) 2.10, TiO2 0.50, total = 96.45 wt. %.
Much of the black-to-green amphibole associated with magnetite at Balls Hill is hastingsite. These hastingsites are potassian (up to 3.5 wt. % K2O) and vary principally in their Fe:Mg ratios (2:1 to 1:5); MnO and ZnO average < 0.5 wt. %. Dr. Robert Popp (personal communication) found 2.45-2.48 wt. % fluorine and reported the ferric-iron/total iron ratio (Fe3+/(Fe2++Fe3+) = 0.28 (± 0.01) in a sample of hastingsite (Betancourt # PPB-2769) from old workings just south of the Fowler Quarry adjacent to Balls Hill.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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