by Robert L. Keefe
from Survey Notes, v.29, no.3, May 1997

All of the following minerals were discovered at the Centennial Eureka mine of the Tintic Mining District in Juab County.

Frankhawthorneite, Cu2Te6+O4(OH)2
Frankhawthorneite is a copper-tellurium hydrate found either isolated or in groups as elongate crystals on drusy quartz in vugs in the waste rock from the mine. Individual crystals are up to 0.1 mm long and are subhedral to euhedral.

Frankhawthorneite is leaf green in color and has a green streak with a vitreous luster and is transparent. X-ray study reveals a monoclinic symmetry. Frankhawthorneite is nonfluorescent under ultraviolet light and is brittle with an uneven fracture. The mineral has a hardness of 3-4 and a density of 5.43 g/cm3.

Frankhawthorneite is found in association with mcalpinite and several Cuand Te-bearing secondary minerals. Frankhawthorneite is named for F.C. Hawthorne of the University of Manitoba.

Jensenite, Cu3Te6+O6 . 2H2O
Jensenite is a copper-tellurium hydrate which occurs as single crystals up to 0.4 mm long or as groups of crystals on white to colorless quartz. The crystals are mainly simple rhombs, some slightly elongate.

The color is transparent emerald green with a green streak and adamantine luster. X-ray study indicates monoclinic symmetry. Jensenite is nonfluorescent and brittle with a uneven fracture and a fair {101} cleavage. It has a hardness of 3-4 and a density of 4.78 g/cm3.

Jensenite is found associated with mcalpinite, xocomecatlite, and several unnamed Cu- and Te-bearing minerals. Jensenite is named for M.C. Jensen who first recognized the mineral.

Leisingite, Cu(Mg,Cu,Fe,Zn)2Te6+O6 . 6H2O
Leisingite is another copper-tellurium hydrate discovered at the Centennial Eureka mine. The mineral was found as isolated hexagonal thin plates or as foliated masses in druses in quartz. Individual crystals average <0.1 mm across and are euhedral to subhedral.

Leisingite's color ranges from pale yellow to pale orange-yellow. It has a pale yellow streak, a vitreous luster, and is transparent. X-ray structure study indicates a hexagonal symmetry. Leisingite is nonfluorescent under ultraviolet light and is brittle to slightly flexible with a perfect {001} cleavage. The mineral has a hardness of 3-4 and a density of 3.41 g/cm3.

Leisingite is found in association with jensenite, cesbronite, and hematite in quartzose dump material. Leisingite was named for J.F. Leising, a geologist who helped collect the discovery specimens.

References
Grice, J.D., Groat, L.A., and Roberts, A.C., 1996, Jensenite, a cupric tellurate framework structure with two coordinations of copper: Canadian Mineralogist, v. 34, p. 55-59.

Grice, J.D., and Roberts, A.C., 1995, Frankhawthorneite, a unique HCP framework structure of cupric tellurate: Canadian Mineralogist, v. 33, p. 649-653.

Roberts, A.C., Grice, J.D., Criddle, A.J., Jensen, M.C., Harris, D.C., and Moffat, E.A., 1995, Frankhawthorneite, Cu2Te6+O4(OH)2, a new mineral species from the Centennial Eureka mine, Tintic district, Juab County, Utah: Canadian Mineralogist, v. 33, p. 641-647.

Roberts, A.C., Grice, J.D., Groat, L.A., Criddle, A.J., Gault, R.A., Erd, R.C., and Moffat, E.A., 1996, Jensenite, Cu3Te6+O6 . 2H2O, a new mineral species from the Centennial Eureka mine, Tintic district, Juab County, Utah. Canadian Mineralogist, v. 34, p. 49-54.

Roberts, A.C., Groat, L.A., Grice, J.D., Gault, R.A., Jensen, M.C., Moffat, E.A.,and Stirling, J.A.R., 1996, Leisingite, Cu(Mg,Cu,Fe,Zn)2Te6+O6 . 6H2O, a new mineral species from the Centennial Eureka mine, Tintic district, Juab County, Utah: Mineralogical Magazine, v. 60, p. 653-657.