FRANCKEITE
Specimen frn-4

Dims: 5.1" x 4.8" x 2.2" (13.0 x 12.2 x 5.6 cm)

Wt: 2 lbs., 13.3 oz. (1.282 kg)

Hulcani Mine, Ancash, Peru

This large specimen consists of a crust made up of tiny metallic Franckeite needles mixed with small cubo-octahedral galena crystals. The Franckeite needles are too small to study easily; one will need at least 30-power magnification to effectively study their triclinic form, as they do not exceed 3 mm in length, and their diameters are smaller than 1 mm. Their gray color and metallic luster makes them rather difficult to determine amidst the somewhat warped galenas. It is evident, though, that there is a large amount of Franckeite present. The crust that they constitute grows out of a slab of base rock that is made up of more massive forms of several different metallic sulfide minerals. There is definitely a lot of galena in it, as well as a noticeable amount of either pyrite or chalcopyrite. The slab's underside is lightly sprinkled with what I believe are many tiny sphalerites. I had never even heard of this mineral until I came across this specimen!

Dims: 2.0 x 1.2 x 0.8" (5.1 x 3.0 x 2.0 cm)

Wt: 1.60 oz. (44.8 g)

San Jose Mine, Oruro, Bolivia

Intergrown clusters of heavily intergrown Franckeite blades make up most of the mass of this thumbnail specimen. Though most of the crystals are exposed and damaged or broken, there are a few in hollows and sheltered areas that appear to be intact. They do not exceed 0.3" (8 mm) in length and have a rather interesting triclinic form- some blades have a sawtooth-edged shape that resembles the outline of a pine tree. All have the standard dark gray coloration and dull metallic luster of the species. A portion of the specimen consists of heavily matted berthierite crystals that partly coat a massive berthierite base that is attached to the Franckeite. There is no host rock present, however.

Dims: 1.5 x 1.3 x 0.8" (3.8 x 3.3 x 2.0 cm)

Wt: 1.84 oz. (52.2 g)

San Jose Mine, Oruro, Bolivia

Several intergrown sprays of radiating Franckeite crystals make up this thumbnail specimen. These crystals are mostly damaged or crushed due to their exposure and softness, but many are still intact. They do not exceed 0.3" (8 mm) in length, but have good triclinic bladed form, with sharp edges and clean faces. All have the standard moderate silvery-gray color and metallic luster, and are opaque, of course. There is no host rock present- the specimen is made up entirely of Franckeite.

Dims: 2.0 x 1.7 x 1.0" (5.1 x 4.3 x 2.5 cm)

Wt: 4.43 oz. (125.7 g)

San Jose Mine, Oruro, Bolivia

This large thumbnail specimen is made up entirely of intergrown Franckeite clusters. These clusters tend to measure approximately 0.4 - 0.8" (1.0 - 2.0 cm), and are in fair to moderate condition, as most of the visible clusters are damaged. The crystals that make up these clusters have only a fair triclinic bladed form due to their intense intergrowth and softness. A few well-defined edges and clean faces are visible, but most edges are rounded and only a few good faces are visible. All have a moderately dark silvery-gray coloration and a slightly dull metallic luster. There is no host rock or any other material present.

Dims: 4.0x3.5x1.8" (10.2x9.0x4.7 cm)

Wt: 24.0 oz. (679g)

Hulcani Mine, Ancash, Peru

The top of this cabinet specimen is covered by countless tiny crystals of frankeite along with more than a hundred small cubo-octahedral galena crystals. The frankeite crystals are large enough to be obvious (some crystals are up to 4mm in length), and there is a lot of this rare mineral here. Under a loupe, the sprays of frankeite grow in random directions, and have a fright metalic luster, and are also irridescent (although this is not visible to the unaided eye). Also, many other minerals are visible, including quartz and some tiny metal sulfide crystals I can't identify (there are several very rare sulfides associated with frankeite). The specimen has a faint sulfur smell, so I suspect the presence of marcasite.

Dims: 5.0x2.3x2.3" (12.7x5.8x5.9 cm)

Wt: 18.3 oz. (518g)

Hulcani Mine, Ancash, Peru

The top of this specimen is covered with frankeite and galena crystals, along with a scattering of other metal sulfides which I have not identified. The frankeite crystals are acicular, and organized in clusters that have random orientations. Under a loupe, the frankeite crystals have a bright metallic luster and are irridescent. The host rock includes veins of pyrite, there are some tiny clusters of quartz, and in a pocket on the bottom are still more unidentified metal sulfides.

Dims: 2.2x1.8x1.1" (5.7x4.5x2.7 cm)

Wt: 2.8 oz. (79.6g)

Hulcani Mine, Ancash, Peru

While most of the surface crust on this specimen appears to be galena crystals, there is enough frankeite to fill the spaces between them. These crystals are organized as sprays of acicular crystals growing between and on the galena. Most of the sparkle is due to the bright luster of the frankeite crystals.