Luis also offered about 20 superb thumbnails which are probably the world's best-yet specimens of the rare sulfosalt pearceite--the arsenic analog of polybasite
which, like that more common species, is apt to form platy, metallic black crystals grouped in rosette-shaped aggregates.
Pyrargyrite stockwork in siderite and quartz-encrusted cavities, together with acanthite, native silver, barite, kaolinite, and museum-quality specimens of polybasite
and stephanite were noted (Jeff Franzen and Ken Watson, pers.
The principal minerals which are found either banded or disseminated within the 90% quartz matrix include pyargyrite, ancanthite, proustite, polybasite
, miargiarite, galena, sphalerite, pyrite, and arsenopyrite.
In the first decade of the 20th century, the Las Chispas mine near Arizpe in Sonora produced some of Mexico's largest and best specimens of polybasite
crystals, large clusters of "poker chip" stephanite crystals, fine acanthite crystal clusters and a few very fine pyrargyrite specimens.
In recent years the Fresnillo area has produced remarkable examples of the silver sulfosalts pyrargyrite, stephanite and polybasite
. Many collectors consider the Romero Fresnillo pyargyrite, known as the "mano" or "hand," to be one of the most aesthetic specimens of any mineral species.
The history of Guanajuato can be traced to a group of Spanish mule skinners who found silver there in 1548, Mining began in 1558 at the San Juan de Rayas mine, which since then has produced large numbers of superb specimens of acanthite, polybasite
and other silver minerals.
The Crown Crescent lode in the Emperor mine has yielded very minor amounts of bournonite, pyrargyrite, proustite and polybasite
. Calaverite was tentatively reported but has not been confirmed.
It is the latter polytype of the As-dominant species pearceite which forms a series with the much commoner Sb-dominant polybasite
The main sulfide minerals are pyrite, galena, sphalerite and chalcopyrite, and much less commonly tetrahedrite and silver sulfosalts (pyrargyrite, proustite and polybasite
Among exhibitors who put in "general" displays of Canadian minerals were the Canadian Museum of Nature; the Smithsonian; the Rice Northwestern Museum; the American Museum of Natural History; Wendy and Frank Melanson; Rod and Helen Tyson (two wide, very spectacular cases); and the Royal Ontario Museum (viewing this case, we learned that there exist brilliant iridescent specimens of stephanite and polybasite
from the Husky mine, Yukon, which are 6 cm across).
Among the best known are the iridescent polybasite
and stephanite specimens produced mostly in the 1960's to 1980's, most notably from the Husky mine.
For earlier scoops on the wonderful iridescent stephanite and polybasite
crystals collected originally in the late 1970's from the Husky mine near Mayo, Yukon Territory, see my show reports from Tucson 1996 (vol.