Minerals of the Sweet Home mine

Undoubtedly the finest and most publicized specimen is the "Alma King," an unprecedented, deep red, single 5 1/2 x 6 1/2-inch rhombohedron that was found in a vug named the "Rainbow Pocket" in the Tetrahedrite Drift on the second crosscut (Fig. 44). This crystal and a 1 1/2-inch companion rhombohedron, are on a matrix plate that measures 23 by 17 inches. It is associated with tetrahedrite, and a concentration of small purple fluorite crystals, along with a small blade of hubnerite. This discovery and another large slab (Fig. 45), with a clustering of five large rhombohedra, is described and illustrated by Moore (1993). The Alma King, described by Murphy (1994) and Voynick (1994b), is on permanent display at the Denver Museum of Natural History.

Gem-clear rhodochrosite crystals are rare but have been found. Up until the mine was reopened in 1992, gem-quality material was very rare. Today, transparent cleavage pieces have yielded handsome faceted gems: the largest known, on exhibit at the Denver Museum of Natural History, weighs 65 carats.

Sphalerite (Zn,Fe)S

Sphalerite is one of the most abundant species found in the Sweet Home mine. It is an important massive component in the ore, and commonly also occurs in crystal pockets as small, wellformed black, green, yellow or red crystals associated with other sulfides and euhedral fluorites and rhodochrosite.

Spionkopite Cu^sub 39^S^sub 28^

Spionkopite is one of the few minerals to be newly identified since the mine was reopened in 1991 (Wenrich and AumenteModreski, this issue). It was found during electron microprobe analysis, associated with bornite, digenite, stromeyerite, and possibly jalpaite.

Svanbergite (see goyazite)

Tetrahedrite/Tennantite (Cu,Fe,Ag,Zn)^sub 12^(SbAs)^sub 4^S^sub 13^

Crystals of tetrahedrite/tennantite from Buckskin Gulch were listed by Endlich (1878) but no further details are reported. Argentiferous tetrahedrite and freibergite were considered among the most important ore minerals responsible for most of the silver in the silver-lead deposits of the Alma district (Singewald and Butler, 1931, 1941; Behre, 1953). Modreski (1988) analyzed selected Sweet Home mine specimens with the "KEVEX" energy-dispersive, X-ray fluorescence spectrometer, and calculated relative percentages of elements contained in the samples. He found that material labeled "freibergite" (DMNH #12467) had only about 1 weight % Ag and is stoichiometrically tennantite. Modreski indicated that "freibergite" should more appropriately be referred to as tetrahedrite/tennantite. See also Wenrich and Aumente-Modreski (this issue) for quantitative electron microprobe analysis of these minerals, and also Raabe and Sack (1984).

Excellent tetrahedrite/tennantite specimens are recognized from the Sweet Home mine. Specimens are attractive, with single euhedral crystals or as intergrown clusters of crystals on sulfide matrix, associated with euhedral rhodochrosite, quartz, fluorite, sphalerite and hunerite. Typically the crystal surfaces are bright and untarnished, often with a distinctive specular appearance. Crystals are generally 1/4 to 1 inch in size, but individual tetrahedrite/tennantite crystals up to 2 inches are known, and fragments of even larger crystals have been seen.