HEMATITE

Fe₂O₃
Hexagonal

	Figure 22-62. Crystal drawings of hematite from Franklin. The drawing at lower center is of a twinned crystal. Drawings are from Palache (1935) who provided crystallographic data.

Hematite is found at both Franklin and Sterling Hill, but is not an economic ore mineral locally. The first report was of pseudocubic partings described and analyzed by Moses (1905); an occurrence of hematite was also noted by Ries and Bowen (1922).

Description

Hematite is found as crystals and as mammillary, botryoidal, and ocherous, massive material. The best crystals from Franklin were described by Palache and Berman (1927) and Palache (1935) (Figure 22-62). The forms are varied, and pseudocubic crystals with complexly formed coigns have been found here; twinning has been observed. The best known of local hematites are specimens bounded by parting planes, yielding highly lustrous pseudocubic fragments, varying from 11 cm (Frondel, 1935) to 17 cm (Frondel, 1972) (Figure 22-63). The parting in such specimens is well-pronounced and appears similar to cleavage, which is absent. No intraparting minerals were noted by the writer, employing microprobe, reflected light, and X-ray studies.

Crystals of hematite are apparently black (very dark red), and fine-grained massive material is dark red. The luster of local material varies from splendent metallic to dull and ocherous. Hematite has been found exsolved in franklinite by Frondel and Klein (1965); they noted several types of exsolution. Carvalho (1978) and Valentino (1983) noted in a study of magnetite- franklinite exsolution intergrowths from Sterling Hill that some magnetite-rich lamellae have been replaced by hematite, and in some cases both magnetite and franklinite have been replaced. Valentino suggested that the former case could have been an example of what was studied by Frondel and Klein (1965).

Composition

Hematite is a ferric-iron oxide mineral. Few analyses are known (Palache, 1935); local material is of near end-member composition, with but a few wt. % FeO and minor Mn. Bauer analyzed one specimen with Fe 54.5, Zn 8.9, Mn 7.0 % and another with 96.08 Fe₂O₃, 1.85 FeO, 0.22 Mn₂O₃, 1.02 MnO, 0.92 ZnO, total = 100.09 wt. %.

Occurrence and paragenesis

Hematite is a minor mineral at Franklin and slightly more abundant at Sterling Hill. In addition to specific assemblages noted below, it also occurs sporadically as grossly and finely disseminated grains in many minerals, including calcite, willemite, and others. Ries and Bowen (1922) and numerous others have reported it replacing franklinite.

	Figure 22-63. Sketch of hematite from Franklin, showing the pseudocubic fragments resulting from partings. Drawing from Palache et al. (1944).

The best known specimens are the large parting fragments from Franklin (Figure 22-63); they have inclusions of franklinite low in Mn (Frondel, 1972) or magnetite and are associated with sparse andradite. Such material was found in the northern end of the Franklin Mine; one specific occurrence was on the 550 level at 760N. Fine crystals are known from the Buckwheat Dolomite (Peters et al., 1983), and many crystals have been found in seams and veins found sporadically in the ores. Superb, splendent, platy crystals, some forming rosettes up to 2 cm, are known from the 300 level, associated with lennilenapeite, magnesioriebeckite, sphalerite, and dolomite. Fine platy crystals up to several cm were also found with rhodonite, calcite, franklinite, and barite. Hematite is also associated with siderite.

At Sterling Hill, hematite is found sparingly in seams and veinlets, but is most abundant in the north orebody, where it occurs as dark-red ocherous to dense material, surrounding franklinite (Figure 12-40), and in convoluted and vein-like assemblages with serpentine, calcite, dolomite, and sphalerite.     

The variety of hematite habits in the north orebody include botryoidal material, layers of specular platy material, and fine-grained blue-black-lustered masses. It occurred in thick masses at contacts with the Franklin Marble adjacent to the Zero fault; much shearing is common in these specimens.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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