WOODRUFFITE

(Zn,Mn²⁺)Mn⁴⁺₃O₇.1-2H₂O
Monoclinic

Woodruffite was first described from Sterling Hill by Frondel (1953) and was included in the study of Potter and Rossman (1979). It has not been reported from Franklin.

Description

Woodruffite occurs as massive, very fine- grained masses and crusts with a mammillary to botryoidal surface. It has a dull luster and is opaque and black to brown. Concentric layering is common, and the hardness varies substantially, from 4½ to 1, the latter in pulverent brown massive material. The density is 3.71 g/cm³ (Frondel, 1953). In reflected light, woodruffite is moderately reflective (R = about 25% in air), distinctly bireflectant, and strongly anisotropic (Ramdohr, 1980). No quantitative optical data are known. Woodruffite resembles todorokite and other massive Mn-oxides; identification is best done employing X-ray methods. Woodruffite was not studied by the writer.

Composition

Woodruffite is a zinc manganese oxide hydrate mineral and is likely the Zn-analogue of todorokite. Frondel (1953) gave the composition as Na₂O 0.06, K₂O 0.55, BaO 0.12, MgO 0.62, ZnO 13.89, MnO 7.88, MnO₂ 64.27, Fe₂O₃ 0.26, Al₂O₃ 0.14, SiO₂ 0.86, H₂O 10.48, total = 99.13 wt. %. No recent analytical studies have been done.

Occurrence and paragenesis

Woodruffite is known from the mud zone at Sterling Hill, mined as the Noble and Passaic Mines in the 1870’s and noted for the abundance of hemimorphite and secondary manganese minerals. Woodruffite occurs as dense masses, intimately associated with chalcophanite and residual franklinite. Confirmed specimens are sparse, but some material probably exists mislabeled in systematic and private collections.

Name

Woodruffite was named for Samuel Woodruff, a miner who was instrumental in preserving many significant specimens.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 11, 2001