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CaTiSiO5
Monoclinic
Titanite was first reported from Franklin by Nuttall (1822) and Vanuxem and Keating (1822b). Specimens are not common from Franklin or Sterling Hill, although titanite is found at both deposits in the magnetite deposits, in the Franklin Marble, and in the gneisses. In general, such rock-forming minerals were undercollected relative to the more exotic local species. The preponderance of specimen material is from the Franklin Marble. Some specimens have been labeled sphene.
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| Figure 15-67. Crystal drawings of two titanite crystals from the Franklin Iron Company Quarry in Franklin. Drawings are from Palache (1935) who provided crystallographic data. | ||
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Franklin titanite has been little studied. Palache (1935) gave morphological data and illustrated some fine crystals. The color is commonly brown; the luster is vitreous to adamantine; and the cleavage is fair to good. It commonly occurs in well-formed, isolated euhedral crystals. The preponderance of such crystals (from x mm up to 5 cm) have typical titanite habit and morphology (Figure 15-67). Frondel (1972) reported crystals up to 15 cm. Bostwick (1992) reported a weak yellow-orange fluorescence in shortwave ultraviolet; many specimens are non-fluorescent.
Titanite is a calcium titanium silicate mineral. Partial microprobe analyses of Franklin titanites indicate that some samples are highly aluminian (up to 8 wt. % Al2O3), and some have 2-5 wt. % FeO. Analysis of a titanite associated with margarite yielded SiO2 31.8, Al2O3 6.74, TiO2 26.28, FeO <0.03, MnO 0.09, MgO 0.14, CaO 33.39, F 1.74, Cl 0.03, H2O+ (calc.) 0.70, less O = F 0.73, corrected total = 100.15 wt. % (Yau et al., 1984).
Many specimens are one-of-a-kind; there is not a special or unique assemblage. Palache reported titanite occurring in pegmatites at both zinc orebodies and in the iron mines, presumably those on Balls Hill.
Franklin specimens are found with both red-fluorescent calcite (from or near the orebody) and non-fluorescent calcite (from the distal Franklin Marble). The best specimens came from the Trotter Mine (Palache, 1935). Commonly associated minerals in orebody specimens include calcite, Ti-free aegirine-augite, andradite, and minor willemite. Commonly associated minerals in marble assemblages include dolomite, fluorite, tremolite, margarite, phlogopite, uvite, pyrrhotite, graphite, and scapolite; fine crystals were found in the Franklin Iron Company Quarry. Frondel (1972) noted that it also occurs in the local gneisses as a common accessory mineral.
At Sterling Hill, titanite was found as dull green blebs in the corundum/margarite assemblage of the Franklin Marble by Dunn (1979c) and Dunn and Frondel (1990), and it also occurs as an accessory mineral with tennantite. Johnson (1990) reported titanite with 4.3 wt. % Al2O3 associated with wollastonite from beneath the east limb on the 1400 level, at the 1060 crosscut.
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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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