Potosíite
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Potosíite is named after Potosí Department, Bolivia where it was discovered in 1980 at the Andacaba deposit, Linares Province.

Discovered in 1980; IMA status: Not Valid (IMA Approved 1981; IMA Discredited 1997)

Chemistry

Chemical Formula:

Pb₆Sn₂⁴⁺Fe²⁺Sb₂⁵⁺S₁₆ 

Lead Tin Iron Antimony Sulfide

Molecular Weight:

2,228.89 gm

Composition:

Iron

2.51 %

Fe

Tin

10.65 %

Sn

Antimony

10.92 %

Sb

Lead

55.78 %

Pb

Sulfur

20.14 %

S

100.00 %

Classification

Mineral Classification:

Sulfides and Sulfosalts

Strunz 8th Ed. ID:

2/C.17-50

Nickel-Strunz 10th Ed. ID:

2.HF.25b

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
H : Sulfosalts of SnS archetype
F : With SnS and PbS archetype structure units

Related to:

Franckeite Group. Sn(II)-poor variety of Franckeite.

Members of Group:

Franckeite Group: Coiraite, Franckeite

Varieties:

None

Synonyms:

IMA1980-057

Crystal Data

Crystallography:

Triclinic - Pinacoidal

Crystal Habit:

As tabular crystals to 3 cm; may be in felted masses.

Twinning:

Rare

Physical Properties

Cleavage:

Perfect on || (001); less perfect on || (010)

Fracture:

n/a

Tenacity:

Brittle

Moh's Hardness:

2.5; Vickers: VHN₁₀₀= 94 - 115 kg/mm²

Density:

6.20 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Bluish gray; grayish black; white in reflected light

Transparency:

Opaque

Luster:

Metallic

Refractive Index:

R1–R2: (400) 38.0–38.9, (420) 37.5–38.5, (440) 37.3–38.2, (460) 37.0–38.0, (480) 36.6–37.7, (500) 36.2–37.4, (520) 35.8–37.1, (540) 35.2–36.7, (560) 34.7–36.3, (580) 34.3–36.0, (600) 33.9–35.7, (620) 33.5–35.5, (640) 33.1–35.3, (660) 32.7–35.0, (680) 32.2–34.7, (700) 31.8–34.4

Birefringence:

0.000 (Isotropic)

Dispersion:

n/a

Pleochroism:

Faint; from bluish gray to yellowish gray

Anisotropism:

Moderate; bluish gray to grayish pale yellow

Occurances

Geological Setting:

On layered sulfide ore in a complex xenothermal-type hydrothermal tin deposit associated with subvolcanic granitic intrusive bodies (Andacaba deposit, Bolivia); in hydrothermal veins cutting rhyolite intrusions into highly kaolinized granite (Herb claim, Canada).

Common Associations:

Galena, Sphalerite, Semseyite, Cerussite, Cassiterite, Quartz (Andacaba deposit, Bolivia); Galena, Pyrite, Sphalerite, Arsenopyrite, Quartz (Herb claim, Canada); Arsenopyrite, Pyrrhotite, Stannite, Jamesonite, Pyrite, Sphalerite, Kutnahorite, Quartz (Hoei mine, Japan).

Common Impurities:

Ag, In

Type Locality:

Andacaba deposit, Linares Province, Potosí Department, Bolivia

Year Discovered:

1980

View mineral photos:

Potosíite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Potosíite is named after Potosí Department, Bolivia where it was discovered in 1980 at the Andacaba deposit, Linares Province. Potosíite was approved as a new mineral species in 1981 by the IMA but later discredited by the IMA in 1997 and redefined as a tin (Sn) poor variety of Franckeite. Similarily, Incaite is a tin-rich variety of Franckeite. Potosíite and Franckeite are two of the rarest sulfosalts in the world. Potosíite had typically been found as massive, uncrystallized granules of less than 1 mm but a find at the San José Mine, Oruro City, Cercado Province, Oruro Department, Bolivia in 2004 produced exceptionally large, highly lustrous, tabular blades (some twinned) of Potosíite measuring up to 13 mm long in association with Franckeite.

Distribution: the type locality [TL] at the Andacaba deposit, Linares Province, Potosí Department, Bolivia. At the San José Mine, Oruro City, Cercado Province, Oruro Department, Bolivia. From the Herb claim, Turnagain River area, Cassiar district, British Columbia, Canada. At the Oploca mine, Pirquitas Ag-Sn Deposit, Rinconada Department, Jujuy, Argentina. From the the Hoei tin mine, Bungo-Ohno City, Oita Prefecture, Kyushu Region, Japan.
 

  
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