Name/Title
PolybasiteEntry/Object ID
2014.1.15Description
Chemical Composition: Al(OH)3
Crystal System: Hexagonal System
Description: Common Name: Polybasite / Stephanite
Chemistry: (Ag, Cu)16Sb2S11 / Ag5SbS4
Group: Sulfides
Location: Unknown
Description: Small specimen with blocky and tabular black crystals with fine needle-like fibers.
Physical Charateristics:
•Color is an iron black to dark gray.
•Luster is metallic.
•Transparency: Crystals are opaque.
•Crystal System: Orthorhombic; 2 m m
•Crystal Habits include tabular or short prismatic crystals that are dominated by prominent pinacoidal faces. Crystals are sometimes intergrown and form pseudohexagonal plates. Also as disseminated grains and massive.
•Cleavage is poor in two directions.
•Fracture is conchoidal to uneven.
•Hardness is 2 - 2.5
•Specific Gravity is approximately 6.2 - 6.3 (heavy even for metallic minerals)
•Streak is a black.
•Other Characteristics: Dark coating can often form after prolonged exposure to light (can be removed by ultrasonic treatment) and crystals tend to be striated perpendicular to the prominent pinacoids.
•Associated Minerals include silver, proustite, pyrargyrite, polybasite, sphalerite, quartz, barite, calcite, pyrite, fluorite, galena, tetrahedrite , acanthite and other silver sulfide minerals.
•Notable Occurrences include Sonora, Mexico; Freiberg, Saxony, Germany; Colorado, California and Comstock, Nevada, USA; Atacama, Chile; Cobalt, Ontario, Canada; Cornwall, England and Bolivia.
•Best Field Indicators are good crystal habit, density, softness, association with other silver sulfosalts and lack of cleavage.
Hardness: 7 Quartz
Rock Type: SedimentaryCollection
RAGM Mineral CollectionAcquisition
Accession
2014.1Source or Donor
Crater Rock Museum (unknown donors)Acquisition Method
GiftDimensions
Height
1-11/16 inWidth
7/8 inLength
1-1/2 inLocation
Location
Display Case
FS-11Room
Frieda Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Curtis GardnerDate
December 27, 2023
