Juanitaite, a new mineral from Gold Hill, Utah

by

Anthony R. Kampf
Mineral Sciences Section, Los Angeles County Museum of Natural History
900 Exposition Boulevard, Los Angeles, California 90007

William. S. Wise
Department of Geological Sciences, University of California
Santa Barbara, California, USA 93106

George R. Rossman
Division of Geological and Planetary Sciences, California Institute of Technology
Pasadena, California, USA 91125

Published in Mineralogical Record, 31, 301-305

Juanitaite from the Gold Hill mine, Gold Hill, Tooele County, Utah, USA Los Angeles County Museum of Natural History specimen number 47573

Abstract

Juanitaite, (Cu,Ca,Fe)₁₀Bi(AsO₄)₄(OH)₁₁·2H₂O, is a new mineral from the Gold Hill mine, Tooele Co., Utah, USA The name is for Juanita Curtis who found the mineral. Juanitaite occurs as square crystal plates with rounded corners in sheaf-like subparallel aggregates and rosettes associated with conichalcite and mixite scattered over fracture surfaces on limonitic matrix. The mineral formed from oxidation of tennantite in quartz veins.

Juanitaite is olive green to grass green with a pale greenish-yellow steak and resinous to dull luster. It is translucent and non-fluorescent. Crystals are tabular on {001} and also exhibit the forms: {110} and {310}. Twinning was not observed. Plates are flexible, but not elastic. Cleavage is perfect on {001} and {110} and good on {100}. Fracture was not observed. The specific gravity measured by sink-float in Clerici solution is 3.61(5) g/cm³. The calculated density is 3.56 g/cm³. Crystals are uniaxial (-), w 1.785(5), e 1.705(5) (white light), but subparallel aggregates yield an anomalous biaxial figure (2V @ 20°). No dispersion was observed. Pleochroism: O = olive brown, E = olive green.
Juanitaite is tetragonal, space group P42/nnm, a = 9.961(3), c = 29.19(2) Å, V = 2896(2) ų, Z = 4. Electron microprobe analyses provided: CaO 8.64, FeO 2.32, CuO 35.97, Bi₂O₃ 14.82, As₂O₅ 29.35, H₂O 8.90 (by difference), total 100.00 wt%. H₂O was confirmed by infrared spectroscopy. Juanitaite has a close chemical relationship with mixite, Cu₆Bi(AsO₄)₃(OH)₆·3H₂O. The six strongest powder diffraction lines are [d(Å)(I)(hkl)] 14.6(100)(002), 7.04(50)(110), 6.34(70)(112), 5.07(50)(114), 3.146(60)(310,303), 2.535(50)(228).

Additional Pictures of Juanitaite

Figure 1. Olive-green crystals of juanitaite covering matrix.

Figure 2. Crystals are typically 0.05 mm wide.

Figure 3. The crystals often are stacks of thin plates.

Figure 4. Interpenetrating crystals show the stack of thin plates.

Figure 5. Spiral growth patterns are common on individual crystals.

Figure 6.  Scanning electron microscope image clearly showing the stack of plates and the spiral growth pattern.
 
 

Infrared Spectrum

The strong absorption in the 3500 cm^-1 region of the infrared spectrum demonstrates that there is water in the mineral.  The raw infrared data are available as a text file (wavenumber, %T).