JAMESITE
Tsumeb Mine, Tsumeb, Namibia (Dana & type locale)
Jamesite is a very rare mineral, described from the Tsumeb Mine in 1981.  It is red-brown in color, acicular to fibrous, and forms radial or sphere-like aggregates, as well as flattened, fan-like sprays, always very small.  The specimens shown at the left are from the original find of Jamesite associated with Tsumcorite, made by Walter Kahn in the 1970’s, which produced the type specimen of Jamesite.  Pricing is according to the richness of the Jamesite, not relative to the size of the matrix.  Chemical composition is: Pb₂ZnFe₂ ³⁺ (Fe ³⁺,Zn)₄(AsO₄)₄(OH)₈(OH,O)_2.   Magnification of 20-50X is required for best appreciation of the crystallization on all specimens.  The acicular, red-brown Jamesite xl. sprays are < 1 mm on all specimens except item E., which has a 2 mm diameter, fan-like spray of acicular Jamesite.  Typical associates are Tsumcorite (Ts, yellow-golden color), Duftite (Du, olive to dark green color), Dolomite (Do, white), Mimetite (M, massive, near white to pale yellow micro xls.), Plancheite (P, acicular, white), and/or Goethite (G, brown to black).  Quartz is often associated as part of the matrix, and micro Quartz xls. are occasionally present.  References: American Mineralogist, 66:1275 (1981),  “Dana’s New Mineralogy”, P. 880, the “Mineralogical Record” magazine, May-June 1982, P. 141, and the “Handbook of Mineralogy”, Vol. IV, P. 263.  Brief descriptions of the specimens follow:

A.  A very small amount of Jamesite (50X required) is on matrix with Dolomite, Duftite, Plancheite, and Goethite.  On the reverse side of the matrix, a rich aggregate of yellow-golden xline Tsumcorite (1/2” X 3/8”) is associated.

B.  The entire top of this specimen is covered with yellow-golden xline and botryoidal Tsumcorite.  Two individual, flat sprays of parallel growth to radially structured Jamesite formed on top of the Tsumcorite – one of the sprays is illustrated here.  Magnification of 20-30X is required.  Associates are minor, all on the back of the matrix.

C.  Two areas on this specimen have sprays of brick red acicular Jamesite.  The best, illustrated here, has black micro spheroids of Goethite associated.  Magnification of 20-30X is required.

D.  A flat, radially structured spray of Jamesite was deposited on yellow-golden, botryoidal / xline Tsumcorite. Magnification of 20-30X is required.  Other associated minerals are present in small amounts.

E.  A flat-laying, fan-shaped spray of brick red acicular Jamesite is on very dark yellow-golden botryoidal Tsumcorite. Magnification of 20-30X is required.  This specimen also has small amounts of massive Tennantite, native Copper and Cuprite, plus at least two unknowns, all present as inclusions within the matrix.

 

POLDERVAARTITE
Wessels Mine, Kalahari Manganese Field, No. Cape Province, South Africa  (Dana and type locale)
Poldervaartite was described as a new mineral from this locality in 1993 and, until very recently, it was regarded as a very rare mineral.  A new find circa 1999-2000 yielded beautifully crystallized specimens!   Poldervaartite typically forms prismatic single crystals (SX), wheat-sheaf crystal groups (WS), or spheroidal aggregates (SP).  Color on these specimens is cream-white, to pale tan.  Ultraviolet fluorescence is deep red under shortwave UV.  The chemical composition is: (Ca,Mn²⁺)₂(SiO₃OH)(OH).  Additional information can be found in “Dana’s New Mineralogy”, Gaines, et al, 1997, P. 1705, “Minerals of South Africa”, Cairncross and Dixon, 1995, P. 231, and “Handbook of Mineralogy”, Vol. II, Part 2, Anthony, et al, 1992, P. 654.

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