LAWSONBAUERITE

(Mn,Mg)₉Zn₄(SO₄)₂(OH)₂₂.8H₂O
Monoclinic, P2₁/c, a = 10.54, b = 9.62, c = 16.46 Å,
b = 95.21^o, Z = 4

	Figure 24-12. Columnar, finger-like groups of lawsonbauerite crystals from Sterling Hill. Field of view is 0.2 mm in maximum dimension.

Lawsonbauerite was described by Dunn et al. (1979a) from Sterling Hill; it has not been found at Franklin.

Crystal structure

The crystal structure of lawsonbauerite was described by Treiman and Peacor (1982). Lawsonbauerite has brucite-like sheets parallel to (100) and composed of octahedrally coordinated Mn and Mg atoms. Two of every nine sites in such sheets are vacant; oxygen atoms at these sites are coordinated to Zn tetrahedra above and below the sheet. The sheets are connected by bonding of these zinc atoms to an interlayer [(Mn,Mg)(OH)₂(H₂O)₄] octahedron. Sulfate groups are loosely held in the interlayer areas. The structure has much similarity to that of mooreite.

Description

Lawsonbauerite occurs as prismatic crystals up to several mm in size and commonly in parallel growth (Figures 24-12 and 24-13); some such aggregates are slightly similar to those of gageite in morphology, forming hand-and-finger-like shapes. Forms present are {001} and {100}. The crystals are flattened parallel to {001} and elongate on [010].

	Figure 24-13. Subparallel, columnar, finger-like groups of lawsonbauerite crystals from Sterling Hill. Field of view is 0.2 mm in maximum dimension.

Lawsonbauerite is colorless to white, but is easily oxidized, and most specimens have brown surficial alterations. Cleavage was not observed in the original description of small crystals, but was later observed by Fred Parker (pers. comm.) and confirmed by the writer. The density is 2.87 g/cm³ (meas.), 2.92 g/cm³ (calc.). Optically, lawsonbauerite is biaxial, negative, with 2V = 42^o, a = 1.590, b = 1.608, and g = 1.611; dispersion is r > v, strong; and the orientation is Y // b, c Ù Z = 7^o in the acute angle beta. There is no discernible fluorescence in ultraviolet.

Composition

Lawsonbauerite is a manganese magnesium zinc sulfate hydroxide hydrate mineral and the Mn-analogue of torreyite. An analysis is given in Table 23, showing the presence of much Mg.

		Table 23. Chemical analyses of mooreite, torreyite, and lawsonbauerite.

Occurrence and paragenesis

Lawsonbauerite was found in the 1570E stope, near the 1300 level of Sterling Hill. It is randomly intergrown with severely altered pyrochroite and sussexite and also associated with zincite, calcite, and franklinite. Subsequent to the original discovery, lawsonbauerite was found in substantial amounts on the 900 level at Sterling Hill.

Name

Lawsonbauerite was named for a distinguished chemist of the New Jersey Zinc Company, Lawson H. Bauer, who described nine new minerals from these deposits, wrote 18 mineralogical papers, and was a substantial contributor to the whole of the local mineral culture. Lawson Bauer’s habit of writing his chemical analyses directly on the unused portion of the studied specimen is among his more significant contributions; it provided unequivocal correlations of data and specimens. Descriptions of his contributions were provided by Frondel (1955) and Mitchell (1982), and they are in part discussed in the section entitled “Cultural aspects of Franklin and Sterling Hill.”

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