ROWEITE

Ca₂Mn₂(OH)₄[B₄O₇(OH)₂]
Orthorhombic, Pbam, a = 9.057, b = 13.357, c = 8.289 Å, Z = 4

Roweite was first described from Franklin by Berman and Gonyer (1937). It was restudied and redefined by Aristarain et al. (1974). It has not been reported from Sterling Hill.

Crystal structure

The crystal structure of roweite was described by Moore and Araki (1974) as having condensed Mn-O octahedra linked by sharing edges and corners to form [Mn²⁺(OH)₂O] sheets. Borax-like [B₄O₇(OH)₂] polyanions are located between the sheets.

Description

According to Aristarain et al. (1974), roweite occurs as 5 mm, light-brown, lath-shaped crystals, elongate on [010] and tabular on {100}. Forms present are {001}, {100}, {201}, {401}, and {021}. The luster is vitreous, and the mineral is very brittle, forming tabular fragments; the cleavages are {100} fair and {001} and {021} poor. The hardness is 4½. Roweite is biaxial, negative, 2V = 28^o, with a = 1.646, b = 1.658, and g = 1.660; dispersion is r < v, strong; absorption is Z > Y > X; and pleochroism is Z = yellowish brown, Y = pale yellow-brown (“amber”), and X = very pale brown to colorless. There is no discernible fluorescence in ultraviolet.

Composition 

Roweite is a calcium manganese boron hydroxide mineral and the Mn-analogue of fedorovskite. The only extant chemical analysis, given by Berman and Gonyer (1937), yielded MnO 28.48, MgO 1.67, ZnO 3.15, CaO 25.55, B₂O₃ 32.59, H₂O 8.56, total = 100.0 wt. % (recalculated after subtraction of insoluble residue). This analysis has approximately 4 % less H₂O than required by the formula proposed by Aristarain et al. (1974) and Moore and Araki (1974).

Subsequent DTA-TGA analysis obtained by the writer yielded 11.9 wt. % H₂O, in very close agreement with the value (12.18 wt. %) required by the structural formula. Microprobe analysis by the writer showed the numbers of octahedral cations, on the basis of a total of 4, to be: Ca_1.91Mg_0.16Zn_0.04Mn_1.89. A separate analysis for boron yielded 30.2 wt. %, in close agreement with the value of 31.38 wt. % required by the structural formula. These analyses confirm the crystal structure determination of Moore and Araki (1974) and indicate that Berman and Gonyer’s data were slightly in error.

Occurrence and paragenesis

Roweite occurs as lath-like crystals, in part replacing calcite and intimately associated with clinochrysotile (Aristarain et al., 1974). These minerals occur in a vein in franklinite, zincite, and willemite. It is a rare mineral locally.

Name

Roweite was named in honor of George Rowe of Franklin, a Mine Captain at Franklin and a dedicated collector of local minerals. His activities are discussed in the section entitled “Cultural aspects of Franklin and Stering Hill” and by Chamberlain and Selden (1986).

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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