= Fluorescent Specimen
= Radioactive Specimen
|FRANCKEITE with ZINKENITE
"D" Vein, 220 Level, San Jose Mine, Dept. of Oruro, Bolivia
The San Jose Mine has become famous for its production of world class specimens of Franckeite, Teallite, Zinkenite, Cylindrite, and other sulfide/sulfosalt minerals, including several of the Silver-bearing sulfosalts. For background information, see the article in the "Mineralogical Record" magazine, May-June 1975 (Vol. 6, No. 3), P. 125-137, entitled "The Mineralogy of the Department of Oruro, Bolivia". Franckeite is described on P. 133. Additional information also appears in the "Handbook of Mineralogy", Vol. I, (1990), P. 160, and in the "Encyclopedia of Minerals", 2nd Edition, Roberts, et al, (1990), P. 293. Two different types are listed below:
TYPE I - In this group, Franckeite was formed as spherical aggregates with a radial structure, i.e., the center of each specimen is the nucleus, from which all of the individual, metallic lead-gray color Franckeite crystals grew. Closely packed Franckeite crystal terminations can be seen protruding out of the backs of the specimens, while the front of each specimen exhibits the internal, radially structured (*), tightly intergrown Franckeite crystal prism faces. Hair-like metallic gray Zinkenite is associated, formed upon the backs of the specimens. The light colored areas seen near the center of item B. are Pyrite. Item D. is a compact intergrowth composed of several of the spheroidal aggregates of Franckeite -- the two largest each measure 5/8" in diameter. None of the specimens have rock matrix. Specimen sizes are given: length X width X thickness, in inches. Order MI-040, Type I A, B, C, or D.
TYPE II - The Franckeite specimens in this group exhibit the same radially structured arrangement of the crystals as the Type I specimens, however, the spheroidal aggregates are complete on all sides. One can see the individual, metallic lead-gray color crystalline Franckeite, and/or small Franckeite crystals, completely covering all surfaces of each specimen. Hair-like metallic gray Zinkenite is associated on all specimens -- magnification of 15-20X is needed for best appreciation of the Zinkenite. On item B., a compact intergrowth, composed of the hair-like metallic gray Zinkenite, protrudes from one side of the otherwise equidimensionally formed spheroid of Franckeite. Item C. has a partial section of a second, radially structured Franckeite crystal group protruding from the side of the main Franckeite crystal spheroid. Item D. is a complete, spheroidal aggregate of Franckeite crystals -- it would look like item I C, if separated so that the center of the crystal group could be observed. Specimen sizes are given: length X width X thickness, in inches. Order MI-040, Type II E, F, G. or H.
Copyright 1998-2017 by Mineralogical Research Co.
All rights reserved.