RETZIAN-(Nd)

Mn₂Nd(AsO₄)(OH)₄
Orthorhombic, Pban, a = 5.690, b = 12.12, c = 4.874 Å, Z = 2

	Figure 25-36. Crystal drawings of crystals of retzian-(Nd), showing forms c {001}, b {010}, m {110}, n {130}, and d {201}. Drawings from Dunn and Sturman (1982).

The first listing of a retzian-group mineral from Sterling Hill was by Moore and Ito (1978). Retzian-(Nd) was described from Sterling Hill by Dunn and Sturman (1982); it has not been found at Franklin.

Description

Retzian-(Nd) occurs as blocky crystals up to 3 mm, elongate on [100]; the forms present are {001}, {010}, {150}, {130}, {110}, {201}, and {021}, and {001} and {010} are the principal forms (Figures 25-36 and 25-37). Aggregates show parallel growth.

Retzian-(Nd) is pinkish brown to reddish brown; color-zoned crystals are common with the darker zone inside the lighter one. The luster is vitreous, and the density is greater than 4.2 g/cm³ (meas.), 4.45 g/cm³ (calc.).

	Figure 25-37. Crystal of retzian-(Nd) from Sterling Hill. This crystal was embedded in calcite and was recovered by dissolution of the calcite in a weak acid solution; the numerous etch pits may have formed in this manner. Field of view is 0.5 mm in maximum dimension.

Optically, retzian-(Nd) is biaxial, positive, 2V = 69^o, with a = 1.774, b = 1.782, and g = 1.798; dispersion is r < v, weak; pleochroism is X = yellow, Y = reddish brown, Z = brown; absorption is Z > Y >> X; and the orientation is X = c, Y = b, and Z = a. It is best identified using both X-ray and quantitative REE analysis.

Composition

Retzian-(Nd) is a manganese neodymium arsenate hydroxide mineral; rare earth elements, chiefly La and Ce, substitute for Nd, and Mg substitutes for Mn. Microprobe analysis yielded: FeO 0.4, MgO 2.0, CaO 0.0, ZnO 1.8, MnO 25.9, As₂O₅ 26.9, La₂O₃ 7.6, Ce₂O₃ 7.8, Y₂O₃ 1.6, Nd₂O₃ 10.9, Pr₂O₃ 4.2, Sm₂O₃ 2.4, Gd₂O₃ 1.9, Eu₂O₃ 0.9, H₂O 8.3 (water value from water content of retzian-(Ce)), total = 102.6 wt. %.

Occurrence and paragenesis

Retzian-(Nd) was originally found on the 700 level, as crystals partly or wholly enclosed in a thin coating of rhodochrosite, which encrusts moderately rich willemite/franklinite  ore.

In addition, two other specimens of retzian-(Nd) were found: one has retzian-(Nd) associated with sonolite, calcite, and sphalerite crystals on willemite/franklinite/calcite  ore; it was found to be Nd-dominant.         

The other occurrence was on the 800 level as light brown crystals, associated with secondary carbonates, willemite, franklinite, zincite, chlorophoenicite, and barite, which coat a massive specimen of pink manganoan calcite. These retzian-(Nd) crystals are chemically inhomogeneous for REE, but Nd is consistently dominant. Some of these light brown crystals are twinned, but were not measured or photographed; the composite twins occur as trillings or sixlings with a distinctly radial, spoke-like arrangement, not unlike some cerussite twins.

Name

Retzian-(Nd) was named in accordance with the Levinson rules for the naming of rare-earth minerals (Levinson, 1966).

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