• Chemistry: (Ag, Cu)16Sb2S11, Silver Copper Antimony Sulfide
  • Class: Sulfides
  • Subclass: Sulfosalts
  • Uses: An ore of silver and as mineral specimens.
  • Specimens

Polybasite is a somewhat uncommon silver bearing mineral. Although not a well known ore of silver, it is never-the-less a locally important ore in some mines. It forms interesting crystals that have a pseudohexagonal outline with rhombohedral striations. Although its symmetry is monoclinic, the nearly hexagonal crystals and striations suggest that it has a higher temperature phase that is hexagonal or trigonal.

Polybasite is in what is called a solid solution series with the mineral pearceite, (Ag, Cu)16As2S11. The two minerals can substitute the antimony for the arsenic within their structures. However, pearceite is far more rare than polybasite possibly indication that antimony is more stable in this structure. The solid solution series is similar to the one for pyrargyrite-proustite. Two other silver sulfosalts.

Polybasite is difficult to distinguish from the minerals hematite, an oxide, and another silver antimony sulfide, stephanite. Hematite forms metallic steel gray platy crystals but has a blood-red streak and is considerably harder. Stephanite lacks the rhombic striations (on the pinacoidal faces), the red flashes and the good cleavage of polybasite.


  • Color is an iron black to a "cherry" red in thin slices with slight flashes of red possibly seen on some crystal surfaces.
  • Luster is metallic.
  • Transparency: Crystals are opaque to translucent in thin slices or at crystal edges.
  • Crystal System: Monoclinic; 2/m
  • Crystal Habits include pseudohexagonal plates or tablets, also massive.
  • Cleavage is perfect in one direction (basal).
  • Fracture is uneven.
  • Hardness is 2 - 3
  • Specific Gravity is approximately 6.1 - 6.3 (heavy even for metallic minerals)
  • Streak is a black to reddish-black.
  • Other Characteristics: Partially malleable, crystals will show a rhombic striation pattern at times and a dark coating can often form after prolonged exposure to light (can be removed by ultrasonic treatment).
  • Associated Minerals include silver, quartz, galena, proustite, pyrargyrite, stephanite, tetrahedrite , acanthite and other silver sulfide minerals.
  • Notable Occurrences include Las Chiapas, Guanajuato and Arizpe, Sonora, Mexico; Saxony, Germany; Colorado and Nevada, USA; Atacama, Chile; Bolivia; Australia and Sardinia.
  • Best Field Indicators are crystal habit, density, softness, cleavage, association with other silver sulfosalts and color.
POLYBASITE specimens:
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POLYBASITE specimen pol-1
$ 45.00
Dims: 0.7" x 0.6" x 0.5" (1.8 x 1.5 x 1.3 cm)
Wt: 4.1 g
Sirena Mine, Guanajuato, Mexico
Many pseudohexagonal platelets are intergrown to make up this Polybasite specimen. All seem to be in good condition, and though it is difficult to be certain due to their intergrowth, I cannot see any obvious damage to the piece. The crystals have good form and measure about 0.3" (0.8 cm) in diameter, maximum. They have a dark gray color and a somewhat dull metallic luster. There are a few tiny prismatic crystals scattered on the Polybasite platelets, but I do not know what they are, and they are too small for me to effectively determine their form. There is also a considerable amount of what appears to be chalcopyrite scattered on the cluster, along with some very tiny, round green globules that I think are made of malachite! I have a feeling that the copper content of these crystals is particularly high. The specimen is affixed inside a domed thimble display box.
no photo
pol-1 ($ 45.00)
Sirena Mine, Guanajuato, Mexico
POLYBASITE specimen pol-2
$ 45.00
Dims: 0.8" x 0.8" x 0.7" (2.0 x 1.8 x 1.8 cm)
Wt: 5.5 g
Sirena Mine, Guanajuato, Mexico
I believe that the dozens of warped hexagonal tabular Polybasite crystals on this specimen are rather rich in copper, judging from the fact that some of them are lightly coated with chalcopyrite. All of them have a dark gray color and a slightly dull metallic luster. It is difficult to tell whether or not the specimen is damaged, as the heavy intergrowth of the crystals tends to warp their form. Accompanying the Polybasites and chalcopyrites are patches tiny round, green globules that I think are made of malachite. It is a very pretty specimen, as the thin chalcopyrite coating gives some of the tabular Polybasites a subtle, colorful sparkle. The specimen is affixed inside a domed thimble box.
no photo
pol-2 ($ 45.00)
Sirena Mine, Guanajuato, Mexico
POLYBASITE specimen pol-3
$ 50.00
Dims: 0.8 x 0.7 x 0.5" (2.0 x 1.8 x 1.3 cm)
Wt: 7.2 g
Guanajuato, Mexico
Two incomplete, intersecting Polybasite blades make up this thumbnail specimen. One is about 70-75% complete, whereas the other is less than 50% complete and is very heavily damaged. The more complete crystal has a discernable monoclinic pseudohexagonal bladed form with 2 intact edges. It appears to be made up of several intergrown blades, one of which is less than 50% complete but not badly damaged. It is coated with a very thin layer of almost microcrystalline chalcopyrite that has a dull golden color- other portions of the specimen are coated with this layer. The Polybasite itself has the standard dark gray color and metallic luster of its species, and is opaque, of course. There is no host rock present.
no photo
pol-3 ($ 50.00)
Guanajuato, Mexico
POLYBASITE specimen pol-4
$ 27.00
Dims: 4.1 x 2.8 x 2.3" (10.3 x 7.1 x 5.8 cm)
Wt: 15.2 oz. (431 g)
Zacatecas City, Zacatecas, Mexico
Several small, rounded Polybasite rosettes rest on the gray base rock of this cabinet specimen. The largest of these rosettes measures about 0.4" (1.0 cm) in diameter and shows the most damage, being the most exposed - some of the blades that make up the rosette are slightly crushed - the others are in excellent condition. All have a dark, black-gray color and a dull luster, though the damaged areas show its metallic luster. The smaller rosettes are difficult to study, as they are coated with tiny quartz crystals. The rosettes themselves rest amid a thick crust of milky-white, crystalline quartz that coats the gray base rock.
no photo
pol-4 ($ 27.00)
Zacatecas City, Zacatecas, Mexico
POLYBASITE specimen pol-5
$ 115.00
Dims: 1.14x0.67x0.59" (2.9x1.7x1.5cm)
Wt: 0.58oz (16.4g)
Fesnillo, Zacatecas, Mexico
This is a nice specimen of polybasite. Its form is a book of thin stacked hexagonal plates, very like hematite can form. However, it does show the charateristic red flashes of polybasite in some places. Unfortunately, none of the hexagonal plates is complete, only 4 sides are visible, as the remainder of the crystal is missing. The polybasite is accompaned by a number of milky-white calcite crystals.
no photo
pol-5 ($115.00)
Fesnillo, Zacatecas, Mexico
POLYBASITE specimen pol-6
$ 60.00
Dims: 1.65x0.71x0.63" (4.2x1.8x1.6cm)
Wt: 0.62oz (17.6g)
Fresnillo, Zacatecas, Mexico
This is a very nice specimen of polybasite (or pearcite, or some intermediate member of this solution series). Most of the mass in the specimen is silvery acanthite (pseudomorphed after argentite). The polybasite occurs as a dozen or more flat plates intergrown with the acanthite. These plates are noticably more "black" than silver, and show red fire. The thinnest of them are actually translucent - you can see a red glow through them, although a loupe is needed to see this. Some of the plates have a hexagonal outline, although most are simply irregular. There are also a dozen or so crystals of a colorless transparent mineral, which has a hexagonal shape but an very complex stepped growth pattern / termination. I thought "quartz" before I used the loupe to examine the mineral. I have seen aquamarines with similar texture and habit, but I don't honestly have any real idea as to what this is.
no photo
pol-6 ($ 60.00)
Fresnillo, Zacatecas, Mexico
POLYBASITE specimen pol-7
$ 39.00
Dims: 0.79x0.59x0.39" (2.0x1.5x1.0cm)
Wt: 40.8ct (8.1g)
Uchucchacua, Lima, Peru
This is a specimen of polybasite. It has polybasite's iron-black color, slight flashes of red, and striations. The crystals appear hexagonal, with rhombohedral striations. There are a few quartz crystals present, also.
no photo
pol-7 ($ 39.00)
Uchucchacua, Lima, Peru
POLYBASITE specimen pol-8
$ 35.00
Dims: 1.03x0.77x0.69" (2.62x1.96x1.76cm)
Wt: 42.0ct (8.1g)
Uchucchacua, Lima, Peru
While there are perhaps a dozen small crystals on this specimen, it is dominated by a single large crystal of polybasite, whose visible dimensions are roughly 9mm on a side. The crystal has a black color with just a hint of red, and distinct red flashes are visible where ever internal fractures are close to the surface. The crystal has a distinct but distorted shape, with clear rhombohedral striations.
no photo
pol-8 ($ 35.00)
Uchucchacua, Lima, Peru


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