The serpentine group

	Figure 18-22. A vein in franklinite-calcite ore (top) is composed of serpentine (dark elongate strips), calcite (stark-white in middle left), and abundant willemite (gray to white). Specimen is 11 cm in maximum dimension. Smithsonian Institution, #R6604. Photo by the author.

The serpentines, hydrous magnesium silicate minerals, are abundant at Franklin and especially so at Sterling Hill. Serpentine was first reported by Fowler (1825), and subsequent studies by Brush (1868), Koenig (1886), Shannon and Larsen (1926), and Foshag (1926) described specific assemblages. Most local serpentine is dark or light brown with a waxy luster. The habit of aggregates may be massive, fibrous, microcrystalline, or hornlike.

Much of the serpentine in the orebodies is manganoan, but few reliable analyses exist. Some dark-colored manganoan material was called vorhauserite; the local application of this name is obscure, but it was considered irrelevant by Palache (1935), and this writer concurs. In spite of their relative abundance, there have been no major studies of serpentines since Palache’s (1935) review. Antigorite, reported as dominant by Frondel (1972), has not been found here by the writer and a co-investigator despite much assiduous searching; Frondel may have used the name antigorite in a broader sense. Baumite was described as a new serpentine mineral by Frondel and Ito (1975), but was discredited by Guggenheim and Bailey (1989, 1990) who found it to be a mixture of 7Å and 14Å minerals including lizardite and chlorite and also containing caryopilite- like and chrysotile-like phases. Hydrorhodonite is discussed under rhodonite.                

	Figure 18-23. Serpentine cementing together fragments of white calcite to form a breccia from Franklin. Specimen is 8 cm in maximum dimension. Smithsonian Institution, #144836. Photo by the author.

Franklin serpentines commonly are late-stage vein minerals and accompany willemite, dolomite, and Mn-carbonates in the carbonate-vein assemblages (Figures 12-45, 18-22, and 23-12) and breccias (Figure 18-23). They also occur in many other niches and assemblages.

At Sterling Hill, serpentine is a pervasive mineral along the east side of the orebody adjacent to the Zero fault. This major fault has introduced abundant Mg-silicate solutions, and replacements of willemite and tephroite are common. Serpentines are very abundant in the north orebody at Sterling Hill, associated with hematite, sussexite, and other minerals (Figure 12-20).

The serpentines are important minerals in both deposits. The locally occurring minerals of the serpentine group are listed below.

Clinochrysotile

Lizardite

Orthochrysotile

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 14, 2001