CARYOPILITE

(Mn,Mg)₃Si₂O₅(OH)₄
Monoclinic

	Figure 18-28. Rosette of caryopilite crystals from Sterling Hill. Field of view is 0.5 mm in maximum dimension.

Caryopilite was first described from Franklin and Sterling Hill by Dunn et al. (1981c). It has been little studied since and, as noted by Guggenheim et al. (1982), it may be a component of some bementite.

Description

Franklin caryopilite is dark reddish brown, massive, and fine-grained; hand-sized specimens are known. Sterling Hill caryopilite occurs in rosettes of pseudohexagonal, 1 mm, platy crystals (Figures 18-28 through 18-31), which have a brownish-orange color. No measurements of physical or optical properties have been made.

	Figure 18-29. Multiple rosettes of superb caryopilite crystals from Sterling Hill. Field of view is 1 mm in maximum dimension.

There is no discernible fluorescence in ultraviolet. It is best distinguished using X-ray methods.

Composition

Caryopilite is a manganese silicate hydroxide mineral. Microprobe analyses of several caryopilites are given in Table 15 and show the variability of its composition.

Contrary to the usual local relations, Franklin caryopilite is much more magnesian than that from Sterling Hill. The analysis of Sterling Hill material is of the rosette-grouped crystals illustrated here. Dunn et al. (1981c) calculated these analyses on the basis of 8 octahedral cations, but it has been shown by Guggenheim et al. (1982) that such data are best calculated on the basis of a serpentine-like formula with octahedral cations to silicon = 9:6. The role of As in caryopilite is uninvestigated to date.

Occurrence and paragenesis

	Figure 18-30. Superb single rosette of Sterling Hill caryopilite composed of hundreds of crystals. Field of view is 0.5 mm in maximum dimension.

The studied Franklin caryopilite occurs in a distinctive, dark reddish-brown, massive intergrowth with calcite, on calcite-willemite-franklinite  ore. There are several generations each of calcite and caryopilite, grown en echelon. Fine crystals of allactite occurs within interstices in the caryopilite-calcite  matrix.

Caryopilite also occurs in small amounts as reddish to pink or brown hemispherules, nodular masses, and clumps, commonly on rhodonite. A caryopilite-like mineral also occurs as a replacement of barite, and a caryopilite-like mineral was observed in the original baumite assemblage by Guggenheim and Bailey (1989). 

	Figure 18-31. Group of caryopilite rosettes from Sterling Hill. Field of view is 1 mm in maximum dimension.

The studied Sterling Hill caryopilite occurs as distinctive rosettes (Figures 18-28 through 18-31) associated with secondary growths of willemite, calcite, sphalerite, and franklinite, on willemite-franklinite- calcite ore.

There may be a number of unrecognized caryopilite occurrences at both Franklin and Sterling Hill.

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