RETZIAN-(La)

Mn₂La(AsO₄)(OH)₄
Orthorhombic, Pban, a = 5.670, b = 12.01, c = 4.869 Å, Z = 2

Retzian-(La) was described by Dunn et al. (1984c) from Sterling Hill; it has not been found at Franklin. 

Description

	Figure 25-35. Crystal drawing of pseudo- hexagonal crystal of retzian-(La) from Sterling Hill. Drawing is from Dunn et al. (1984c).

Retzian-(La) occurs as small (<1 mm) pseudohexagonal crystals, tabular on {001} with {001}, {010}, and {110} as the major forms and {150} subordinate in development (Figure 25-35). The luster of crystal faces is variable; most are dull, but {010} is vitreous, as are fracture surfaces. Retzian-(La) is dark reddish brown, transparent, and has a density of 4.2 g/cm³ (meas.), 4.49 g/cm³ (calc.). Cleavage was not observed. It is best identified by both X-ray and chemical methods.

Optically, retzian-(La) is biaxial, positive, 2V = 82^o, with a = 1.766, b = 1.773, and g = 1.788, and strong dispersion, r > v. Pleochroism is patchy, varying from pale brown to pale violet-brown; absorption is Z > Y > X; and the orientation is X = c, Y = b, Z = a. There is no discernible fluorescence in ultraviolet.

Composition

Retzian-(La) is a manganese lanthanum arsenate hydroxide mineral; rare earth elements, chiefly Ce and Nd, proxy for La, as does Y, and Mg substitutes for Mn. Microprobe analysis yielded: MnO 25.2, MgO 3.7, ZnO 1.2, As₂O₅ 26.5, La₂O₃ 10.6, Ce₂O₃ 8.8, Nd₂O₃ 8.2, Pr₂O₃ 5.1, Sm₂O₃ 2.2, Y₂O₃ 2.5, H₂O 7.7 (calculated), total = 101.7 wt. %.

Occurrence and paragenesis

Retzian-(La) was found but once, in the central zincite zone at Sterling Hill, as euhedral crystals associated with secondary willemite, on a todorokite- covered vein surface in red-willemite/franklinite  ore containing much calcite.

Name

Retzian-(La) was named in accordance with the Levinson system for naming rare earth minerals (Levinson, 1966).

 

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