GOETHITE

FeO(OH)
Orthorhombic    

	Figure 22-56. Bladed goethite crystals on acicular rutile crystals from the Buckwheat Dolomite. Field of view is 0.2 mm in maximum dimension. Photograph courtesy of Tom Peters and the Paterson Museum.

Goethite was reported from the Buckwheat Dolomite by Palache (1935), and much of the material he called limonite is likely goethite. It is known from both Franklin and Sterling Hill.

Description

Goethite is invariably brown; much local material is fibrous in habit, but some occurs as well-crystallized, bladed crystals in subparallel to divergent fasicles (Figure 22-56). Peters et al. (1983) illustrated many habits of goethite crystals from the Buckwheat Dolomite. The bulk of local goethite is massive; some specimens have botryoidal to mammillary surfaces; and much local material is ocherous. Fist-sized masses are known. No physical data have been obtained.

Composition

Goethite is an iron oxide hydroxide mineral. One analysis of Franklin goethite (brown with black mammillary surface), performed by Lawson Bauer, yielded 2.48 wt. % Mn, 49.8 wt. % Fe, and 5.15 wt. % Zn. 

Occurrence and paragenesis

Goethite is not a major mineral locally. It is a mineral of weathering and alteration environments. It was found in the oxidized zone at the north end of the Franklin Mine, in the Buckwheat Dolomite, and as a matrix for secondary copper carbonates on the 200 level.

At Sterling Hill, goethite is common in the oxidized material from the surface pit workings, occurring as hollow nodules associated with hetaerolite, chalcophanite, and hemimorphite. The paucity of significant specimens may be due in part to the perceived unattractiveness of such specimens.

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