New Utah Minerals: Juanitaite & Dickthomssenite

By Carl Ege

Juanitaite, (Cu,Ca,Fe)10Bi(AsO4)4(OH)10· 2H2O

Juanitaite is a hydrated copper-calcium-iron-bismuth-arsenate hydroxide found on the 30- and 150-foot levels of the Gold Hill mine in Tooele County. The mineral is found as square plates or as crystallized aggregates. Individual crystals are up to 150μm long and 1μm wide. Juanitaite is olive-green to grass-green and has a pale greenish yellow streak. X-ray studies show a tetragonal symmetry. The mineral has a hardness of 1 and a density of 3.61 g/cm3.

On the 30-foot level, juanitaite is associated with conichalcite, chrysocolla, azurite, gold, quartz, and mixite. On the 150-foot level, the mineral occurs with connelite, tyrolite, and azurite. Juanitaite is named for Juanita Curtis who discovered the mineral.

Dickthomssenite, Mg(V2O6)· 7H2O

Dickthomssenite is a hydrated magnesium vanadate found at the Firefly-Pigmay mine in San Juan County. The mineral is found as needle-like to platy prismatic crystals. Individual crystals are up to 1.5 mm long and 0.5 mm wide. Dickthomssenite is light golden brown, has a white streak, and a vitreous luster. X-ray studies show a monoclinic symmetry. Dickthomssenite has a hardness of 2.5 and a density between 1.96 and 2.09 g/cm3.

Dickthomssenite occurs as thin coatings on sandstone, approximately 960 feet from the main portal of the mine. The mineral is associated with pascolite, sherwoodite, and native selenium. Dickthomssenite is named for Richard W. Thomssen, a consulting geologist from Nevada.

For more information

Hughes, J.M., Cureton, F.E., Marty, J., Gault, R. A., Gunter, M.E., Campana, C.F., Rakovan, J., Sommer, A., and Brueseke M.E., 2001, Dickthomssenite, Mg(V2O6)· 7H2O, a new mineral species from the Firefly-Pigmay mine, Utah – descriptive mineralogy and arrangement of atoms: The Canadian Mineralogist, v. 39, p. 1691-1700.

Kampf, A.R., Wise, W.S., and Rossman, G.R., 2000, Juanitaite, a new mineral from Gold Hill, Utah: Mineralogical Record, v. 31, p. 301-305.

Survey Notes, v. 34 no. 3, September 2002