WALLKILLDELLITE

Ca₄Mn³⁺₄Mn²⁺₂As⁵⁺₄O₁₆(OH)₈.18H₂O 
Hexagonal, P6₃/mmc, P62c, or P6₃mc,
a = 6.498, c = 22.78 Å, Z = 1

Wallkilldellite was described by Dunn and Peacor (1983a) from Sterling Hill; it has not been found at Franklin.

Description

Wallkilldellite occurs as flattened radial clusters of dark red, platy, 0.1 mm crystals with perfect {0001} cleavage and vitreous luster. The density is 2.85 g/cm³ (meas.), 2.90 g/cm³ (calc.). It is slightly similar to mcgovernite, kraisslite, and the unnamed Fe³⁺ analogue of hematolite, but is much redder than these minerals. It is best differentiated using X-ray methods.

Optically, it is uniaxial, negative, with w = 1.728; e could not be determined due to the thinness of the platy crystals. Wallkilldellite is pleochroic with O = reddish orange, E = light orange pink; absorption is moderate, O > E.

Composition

Wallkilldellite is a calcium manganese arsenate hydroxide hydrate mineral and is isostructural with kittatinnyite. A microprobe analysis, with water by difference, is presented in Table 25.

Occurrence and paragenesis

Wallkilldellite was found in approximately 1974 at Sterling Hill near the 340 level. The matrix is franklinite/willemite/calcite  ore, the surface of which is coated with carbonates, followed by a cuproan, manganoan adamite which is present as a light yellow-green fibrous coating.

Wallkilldellite is the last mineral to form in this assemblage, occurring as 0.5 mm aggregates of platy crystals. It is quite rare. See discussion for kittatinnyite.

Name

Wallkilldellite is named for the valley (dell) of the Wallkill River, where both deposits cropped out in full view.

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