Names
Sicherite
Intro
Sicherite is an exceedingly rare thallium arsenic sulfosalt mineral belonging to the orthorhombic crystal system, first discovered in the cavities of Triassic dolomites at the famed Lengenbach Quarry, Switzerland.
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Basic Information Show Hide
Mineral ID
sicherite
Common Synonyms / Aliases
IMA 1997-051
Chemistry Show Hide
Chemical Formula
TlAg₂(As,Sb)₃S₆
Elements
Tl, Ag, As, Sb, S
Minor Elements / Impurities
Cu, Fe
Empirical Formula
Tl₁.₀₀As₃.₀₀S₅.₀₀
Molecular Weight (g/mol)
589.44
Solubility
Insoluble in water
Reaction to Acid
Slow reaction with hot concentrated nitric acid
Classification Show Hide
Mineral Type
Mineral Species
IMA Status
Approved
IMA Symbol
Sic
Strunz Classification
02.HD.55 (Nickel-Strunz 10th ed: 2.HD Sulfosalts of SnS archetype, with Tl)
Dana Classification
03.04.14.01
Mineral Group
Sulfosalts (Tl-As sulfosalts)
Crystal Structure Show Hide
Crystal System
Orthorhombic
Crystal Habit
Prismatic to tabular crystals, typically elongated along [001]
Crystal Class
mmm (2/m 2/m 2/m) - Dipyramidal
Space Group
Pmnb (Pnam)
Cell Parameter A (Angstrom)
12.479
Cell Parameter B (Angstrom)
15.522
Cell Parameter C (Angstrom)
5.719
Cell Angle Alpha (Degrees)
90
Cell Angle Beta (Degrees)
90
Cell Angle Gamma (Degrees)
90
Unit Cell Z
4
Crystal Twinning
None observed
Common Crystal Faces
{100}, {010}, {001}, {110}
Physical Properties Show Hide
Common Colors
Dark grey, Black, Dark lead-grey
Streak
Dark reddish-brown to black
Luster
Metallic to sub-metallic
Transparency / Diaphaneity
Opaque
Hardness (Mohs)
2.5 - 3
Cleavage
Distinct
Cleavage Direction
{010}
Cleavage Angle / Parting Quality
Distinct on {010}
Fracture
Uneven to sub-conchoidal
Tenacity
Brittle
Specific Gravity
5.26 - 5.28
Magnetism
Non-magnetic
Melting Point
N/A (decomposes upon heating)
Thermal Stability
Decomposes at elevated temperatures releasing volatile arsenic and sulfur fumes
Optical Properties Show Hide
Optical Axial Angle (2V)
N/A
Optical Sign / Extinction
N/A
Dispersion
Strong in reflected light
Optical Character
Biaxial+
Pleochroism
Distinct in reflected light (greyish-white to slightly brownish-white)
Pleochroism Details
Distinct reflection pleochroism in plane-polarized reflected light
Optical Phenomena
Strong anisotropy with reddish internal reflections
Fluorescence
Inert under SW/LW ultraviolet light
Luminescence / Phosphorescence / Thermoluminescence
Non-fluorescent
Absorption Spectrum
N/A
Occurrence and Formation Show Hide
Formation Process
Hydrothermal sulfosalt mineralization formed during late-stage hydrothermal processes in white dolomite cavities.
Geological Environment
Hydrothermally altered Triassic dolomitic marbles.
Associated Minerals
Realgar, Orpiment, Hatchite, Edenharterite, Sartorite, Hutchinsonite, Pyrite, Dolomite
Type Locality
Lengenbach Quarry, Imfeld, Binn Valley, Valais, Switzerland
Major Producing Countries / Localities
Switzerland
Economic Deposit Type
Hydrothermal dolomite-hosted sulfosalt deposit
History and Naming Show Hide
Discovery Year
1997
Name Origin
Named in honor of Valentin Sicher (born 1925), a Swiss mineral collector and specialist on Lengenbach minerals.
Type Specimen Repository
Natural History Museum of Basel, Switzerland; Musée Cantonal de Géologie, Lausanne, Switzerland
Safety and Related Information Show Hide
Wearability
Poor
Health Hazards
Highly toxic. Contains thallium (Tl) and arsenic (As). Chronic or acute ingestion/inhalation hazards.
Handling Precautions
Handle with gloves and protective gear. Avoid inhaling dust particles. Wash hands thoroughly after handling. Store in a secure, sealed, and labeled container away from food and children.
Varieties
None
Polytypes
None
Related Minerals
Edenharterite (TlPbAs₃S₆), Bernardite (TlAs₅S₈), Lorándite (TlAsS₂), Hutchinsonite (TlPbAs₅S₉)
Commercial and Gemology Show Hide
Common Treatments
None
Enhancements
None
Common Cuts
None (Collector/Scientific specimen only)
Rarity / Market Grade
Extremely rare collector / Research specimen
