YEATMANITE Chapter15. Nesosilicates

YEATMANITE

[Mn₅Sb₂][Zn₆Mn₄(Si_3.8Fe³⁺_0.2)]O₂₈.
Triclinic, P1, a = 5.443, b = 11.683, c = 9.134 Å,
a = 92.06, b = 101.19, g = 76.34^o, Z =1.

Yeatmanite was first described by Palache et al. (1938) from Franklin. Dunn and Leavens (1980) provided additional chemical, optical, and paragenetical data and the first X-ray powder data. Yeatmanite is known from both Franklin and Sterling Hill.

Crystal structure

Moore (1966) noted a structural relation to katoptrite, indicated it is a stuffed pyrochroite structure, and proposed a new formula. Moore et al. (1976) expanded this description, describing yeatmanite as a derivative structure of katoptrite. The crystal structure was described in detail by Kato (1986), using material studied by Dunn and Leavens (1980) and confirming Moore’s model. Yeatmanite has an octahedral sheet consisting of [5 Mn and 2 Sb], sandwiched by upper and lower tetrahedral sheets consisting of Zn₃Mn₂Si₂.

Description




	Figure 15-94. Crystal drawing of twinned yeatmanite from Franklin, showing the forms a {100}, b {010}, and n {210}; the twin plane is {023} (Palache et al., 1938).

Yeatmanite occurs as lath-like crystals, almost invariably platy and wholly enclosed in other species. Maximum crystal size is approximately 1 cm (HU# 92878 and Paterson Museum # F-731), but most are quite small. Crystals rarely can be pseudohexagonal, and a common habit was illustrated by Palache et al. (1938). Yeatmanite is medium brown to dark brown, with vitreous luster, perfect {001} cleavage, and a density of 5.04 g/cm³. Optically, it is biaxial, negative, 2V = 40^o, with a = 1.873, b = 1.905, and g = 1.910; dispersion is moderate r < v; and pleochroism is absent. There is no discernible fluoresence in ultraviolet. Yeatmanite can be confused locally with ganophyllite (which is easily distinguished by its softness), bannisterite, and franklinfurnaceite. All three minerals have unique X-ray powder patterns, and additionally, none is known to occur in the host assemblages for yeatmanite.

Composition

Yeatmanite is a manganese zinc antimony silicate mineral related to catoptrite. Representative microprobe analyses of Franklin material from Dunn and Leavens (1980) are given in Table 3 and show the range of composition. Kato (1986) proposed that in his studied specimen Mn and Zn are fully ordered, but left open the possibility that there may be disorder in other specimens in which the composition has been shown to vary slightly. Sterling Hill yeatmanite has not been fully analyzed, but energy-dispersive microprobe analysis showed it to have a composition nearly identical to Franklin yeatmanite. Yeatmanite is only slightly invariant in composition, compared with the other Sb-bearing mineral here, romeite, which is host to variable amounts of non-essential, large cations.

Occurrence and paragenesis

Yeatmanite was first found at Franklin in willemite associated with massive pink sarkinite in a vein assemblage. This yeatmanite occurs within both willemite and sarkinite, but only where they are in contact. A second occurrence was found by John L. Baum, Resident Geologist at the Franklin Mine, at slightly below the 750 level; detailed locality data are given by Dunn and Leavens (1980). In this assemblage, it occurs as euhedral crystals, associated with diopside, andradite, and romeite, in a white matrix of massive johnbaumite. Yeatmanite has also been found with willemite and calcite in a vein in massive franklinite. In 1985, a specimen was found on the Buckwheat Dump which consisted of a layered sequence consisting of bands of (1) calcite and franklinite, (2) franklinite, and (3) a Ca-As apatite (likely johnbaumite) containing franklinite and yeatmanite.

Yeatmanite was found at Sterling Hill in 1980, as tiny brown platy crystals in two assemblages, both occurring in calcite-rich franklinite-willemite ore. It was found with willemite, adelite, and barite on the 1500 level and with tilasite, fluoborite, calcite, and willemite on the 1200 level. Although considered a rare mineral, it is likely, given its composition, that yeatmanite occurred widely distributed through both orebodies, occurring in response to localized Sb and Mn concentrations.

Name

Yeatmanite was named in honor of Pope Yeatman, a distinguished mining engineer.

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