HEDYPHANE

Ca₂Pb₃(AsO₄)₃Cl
Hexagonal

	Figure 25-2. Crystal drawing of hedyphane from Franklin. Drawing is from Palache (1935) who provided crystallographic data.

Hedyphane was described from Franklin by Foshag and Gage (1925), and fine crystals were later described by Palache and Berman (1927) and Palache (1935). Hedyphane is not known from Sterling Hill, but at Franklin it is the most abundant secondary host for both Pb and As.

Description

Hedyphane occurs as superb gray to colorless crystals, up to at least 3 mm, bipyramidal in habit, and tabular on [0001] (Figure 25-2). Most hedyphane, however, is massive, granular, and orange to yellow orange or colorless, although gray material has been reported. The density is 5.85 g/cm³. The luster is decidedly greasy to adamantine. Optically, hedyphane is uniaxial, positive, with w = 1.948 and e = 1.958 (Palache and Berman, 1927) or uniaxial, negative (Palache, 1935). As first noted by Palache (1928b), hedyphane is fluorescent in ultraviolet. It has a moderate orange color in shortwave and a weak yellowish white color in longwave. It is best distinguished from other As-apatites by X-ray methods and chemical analysis.

Composition

Hedyphane is a calcium lead arsenate chloride mineral of the apatite group. Rouse et al. (1984) showed that Ca and Pb are ordered in the structure with the ratio Pb:Ca = 3:2. The statement of the writer (Dunn et al., 1980a) that much local material is calcian mimetite was superceded by his statement, in the study of Rouse et al. (1984), that mimetite is rare and that hedyphane is the predominant Ca-Pb-As apatite-group phase here. Numerous analyses of local material by the writer were given by Rouse et al. (1984) showing the partial solid solution towards mimetite and turneaureite (the latter then-unnamed and listed as # C6270-1 and C6270-2). Franklin hedyphane is a significant host for Sr in secondary veins; the analyses given in Table 24 are selected to show the range of Sr substitution in hedyphane from here. Långban hedyphane, in contrast, carries Ba as a guest element.

Occurrence and paragenesis

Hedyphane occurs as a secondary vein mineral; its genesis is uncertain. The original occurrence was between the 500 and 600 levels in the east limb at Franklin, from which also came chlorophoenicite and schallerite. Here hedyphane occurred as white to colorless massive material, associated with green willemite, pink rhodonite, tarnished copper crystals, and calcite in veins in franklinite/willemite  ore; fine, hexagonal, 6 mm, barrel-shaped crystals occur in this assemblage. Palache and Berman subsequently described fine crystals associated with cahnite, tabular willemite, barite, rhodonite, and manganaxinite from a vein assemblage.

Hedyphane occurs in a number of assemblages; only those generally recognized as being common are mentioned here. It occurs in a brecciated vein assemblage of barylite with copper, willemite, serpentine, and white, platy, curved calcite. It also occurs with andradite, rhodonite, and willemite in quite varied vein assemblages. Brownish “ribbon” veins of rhodonite crystals with hedyphane are not uncommon; many were mislabeled as schallerite in earlier years. In general, hedyphane has an apparent affinity for rhodonite; willemite and unstudied fibrous amphiboles are also commonly associated.

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