WAWAYANDAITE

Ca₁₂Mn₄B₂Be₁₈Si₁₂O₄₆(OH,Cl)₃₀ 
Monoclinic, P2/c or Pc, a = 15.59, b = 4.87, c = 18.69 Å,
b = 101.84^o, Z = 1

	Figure 19-10. Curved platy crystals of wawayandaite from Franklin. Field of view is 0.8 mm in maximum dimension.

Wawayandaite was first described by Dunn et al. (1990) from Franklin. It is not known from Sterling Hill or elsewhere. The crystal structure has not been investigated.

Description

Wawayandaite occurs as colorless platy crystals; some are euhedral, sharp, tabular on {100}, and twinned on (100), but these are rare. Most crystals are severely curved and are very thin and transparent (Figure 19-10). Locally, wawayandaite resembles some diaphanous, late-stage barysilite (Figure 16-4), talc, or prehnite. Wawayandaite is also known in exceedingly fine-grained, clay-like aggregates. Wawayandaite is colorless, but may appear white or silvery in the aggregate.

The luster is very pearly on curved crystals and slightly pearly on euhedral crystals and clay-like aggregates; cleavage is perfect, apparently on {100}. Wawayandaite is extremely soft. Density determinations are unreliable; the calculated density is 2.98 g/cm³.

Optically, wawayandaite is biaxial, negative, with 2V = 85.2^o. The indices of refraction are a = 1.619 (calc.), b = 1.631, and g = 1.641; dispersion is strong, r < v. The orientation is X L a = 11.5^o within the obtuse beta angle, Y // b, Z // c. There is no discernible pleochroism or fluorescence in ultraviolet.

Composition

Wawayandaite is a calcium manganese boron beryllium silicate hydroxide-chloride mineral and is not known to be related to other species. The chemical composition is SiO₂ 28.2, MgO 1.9, CaO 24.8, ZnO 1.1, MnO 9.8, B₂O₃ 3.8, BeO 17.6, H₂O 9.6, Cl 3.0, less O = Cl 0.7, total = 99.1 wt. %.

Occurrence and paragenesis

Wawayandaite occurs in a classic Franklin vein assemblage consisting of druse andradite on calcite-poor franklinite-willemite  ore. Superb 6 x 1 mm, prismatic willemite crystals and 5 mm, equant, rhombic calcite crystals occur on this druse. These are partially coated with a druse of dull reddish-brown friedelite. Hodgkinsonite crystals and twinned cahnite crystals are rarely associated. Wawayandaite occurs last in this assemblage, in all of the above-cited habits. These specimens were found prior to 1923; they were in collectors’ hands by then. This mineral was likely preserved by serendipity, as a minor mineral associated with superb, attractive willemite crystals.

Wawayandaite was noted by the writer in another assemblage, preserved only as a micromount mineral specimen. In this assemblage, franklinite ore is irregularly coated by a calcite druse followed by pyrochroite crystals and, separately, by a pink sussexite druse intergrown with brown prismatic gageite which persists through the sussexite crystallization sequence. Wawayandaite is the latest mineral to form, occurring intergrown with gageite, and persisting after gageite has formed. In this assemblage it occurs as slightly fibrous, curved, white aggregates.

Wawayandaite was found in yet a third assemblage in which it occupies vugs in altered willemite-franklinite-andradite  ore. The vuggy areas are coated with druses of hodgkinsonite and fluorite; wawayandaite occurs as platy pearly crystals occurring on these previously formed minerals.

Name

Wawayandaite was named in allusion to its grossly curved habit. In the language of the indigenous Lenni Lenape Indians, the word “wawayanda” means “many or several windings.”

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