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Keutschite

A valid IMA mineral species
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04137790017272005897740.jpg
Keutschite

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
09206550017272005935909.jpg
Keutschite

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
03195440017272472472413.jpg
Keutschite, etc.

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
04137790017272005897740.jpg
Keutschite

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
09206550017272005935909.jpg
Keutschite

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
06214440017866685366982.jpg
Keutschite, etc.

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
04137790017272005897740.jpg
Keutschite

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
09206550017272005935909.jpg
Keutschite

Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
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About KeutschiteHide

05093590017272472483881.jpg
Dr. Frank Keutsch
Formula:
Cu2AgAsS4
Colour:
grey colour with a slight green-brassy tint
Lustre:
Metallic
Hardness:
4 - 5
Specific Gravity:
4.663 (Calculated)
Crystal System:
Tetragonal
Member of:
Stannite Group
Name:
Named for Dr. Frank Keutsch (b. 1971), professor of chemistry at Harvard University and specialist in sulphides and sulphosalts.
Can be considered a partially Ag-substituted luzonite.

Compare the chemically similar eckerite.


Unique IdentifiersHide

Mindat ID:
46159
Long-form identifier:
mindat:1:1:46159:9

IMA Classification of KeutschiteHide

Classification of KeutschiteHide

Strunz-mindat (2026):
2.KA.10

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
K : Sulfarsenates, Sulfantimonates
A : Sulfarsenates with (As,Sb)S4 tetrahedra

Mineral SymbolsHide

As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.

SymbolSourceReference for Standard
KeuIMA–CNMNCWarr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43

Physical Properties of KeutschiteHide

Lustre:
Metallic
Transparency:
Opaque
Colour:
Grey colour with a slight green-brassy tint
Streak:
Black
Hardness:
4 - 5 on Mohs scale
Hardness:
VHN25=352 - 380 kg/mm2 - Vickers
Tenacity:
Brittle
Cleavage:
None Observed
Fracture:
None observed
Density:
4.663 g/cm3 (Calculated)

Optical Data of KeutschiteHide

Anisotropism:
greenish grey to grey
Bireflectance:
weak
Reflectivity:
WavelengthR1 (%)R2 (%)
470nm25.2%26.1%
546nm29.6%29.4%
589nm29.4%29.2%
650nm28.5%28.6%


Graph shows reflectance levels at different wavelengths (in nm). Peak reflectance is 29.6%.
R1 shown in black, R2 shown in red
Colour in reflected light:
grey
Internal Reflections:
none
Pleochroism:
Weak

Chemistry of KeutschiteHide

Mindat Formula:
Cu2AgAsS4
Element Weights:
Element% weight
S29.274 %
Cu29.007 %
Ag24.620 %
As17.100 %

Calculated from ideal end-member formula.
Elements listed:
Ag, As, Cu, S - search for minerals with similar chemistry

Crystallography of KeutschiteHide

Crystal System:
Tetragonal
Class (H-M):
42m - Scalenohedral
Space Group:
I42m
Setting:
I42m
Cell Parameters:
a = 5.5834(15) Å, c = 10.021(3) Å
Ratio:
a:c = 1 : 1.795
Unit Cell V:
312.40 ų (Calculated from Unit Cell)
Z:
2

X-Ray Powder DiffractionHide

Geological EnvironmentHide

Paragenetic Mode(s):
Paragenetic ModeEarliest Age (Ga)
Stage 3b: Earth’s earliest hydrosphere>4.45
12 : Hadean hydrothermal subsurface sulfide deposits (see also #33)

Type Occurrence of KeutschiteHide

Type Locality:
ⓘ Uchucchacua Mine, Uchucchacua area, Oyón District, Oyón Province, Lima, Peru
General Appearance of Type Material:
blocky, free-standing crystals up to 3 mm
Place of Conservation of Type Material:
Type material is deposited in the reference collection of the Naturhistorisches Museum Wien, Wien, Austria, specimen number N9734
Geological Setting of Type Material:
manganese rich zone
Associated Minerals at Type Locality:
AlabanditeAlabanditeManganoquadratiteProustiteBillingsleyite
DiaphoriteDiaphorite
Reference:
Topa, Dan; Takagi Fredrickson, Rie; Stanley, Chris; Dincă, George (2026) Keutschite, Cu2AgAsS4, a new mineral with a stannite structure from the Uchucchacua polymetallic deposit, Lima Department, Peru. European Journal of Mineralogy, 38 (1). 1-7 doi:10.5194/ejm-38-1-2026

Synonyms of KeutschiteHide

Other Language Names for KeutschiteHide

German:Keutschit

Relationship of Keutschite to other SpeciesHide

Member of:
Stannite Group
Other Members of Stannite Group:
BriartiteCu2FeGeS4Tet.
ČernýiteCu2CdSnS4Tet. 42m : I42m
FamatiniteCu3SbS4Tet. 42m : I42m
FerrokësteriteCu2FeSnS4Tet. 4 : I4
HocartiteAg2(Fe2+,Zn)SnS4Tet. 42m : I42m
KësteriteCu2ZnSnS4Tet. 4 : I4
KuramiteCu3SnS4Tet. 42m : I42m
LuzoniteCu3AsS4Tet. 42m : I42m
OmariniiteCu8Fe2ZnGe2S12Orth. 222 : I222
PermingeatiteCu3SbSe4Tet. 42m : I42m
Petrukite(Cu,Fe,Zn,Ag)3(Sn,In)S4Orth. mm2 : Pmn21
PirquitasiteAg2ZnSnS4Tet. 4 : I4
RichardsiteZn2CuGaS4Tet. 42m : I42m
StanniteCu2FeSnS4Tet. 42m : I42m
StannoiditeCu+6Cu2+2(Fe2+,Zn)3Sn2S12Orth. 222 : I222
'UM1984-30-S:CuFeSn'Cu2Fe2Sn3S7
'Unnamed (Cu-Zn-In Sulphide)'CuZn2InS4
VelikiteCu2HgSnS4Tet. 4 : I4
ZincobriartiteCu2(Zn,Fe)(Ge,Ga)S4Tet. 42m : I42m

Common AssociatesHide

Associations Based on Photo Data:
4 photos of Keutschite associated with ProustiteAg3AsS3
4 photos of Keutschite associated with AlabanditeMnS
2 photos of Keutschite associated with RhodochrositeMnCO3
2 photos of Keutschite associated with ManganoquadratiteAgMnAsS3
2 photos of Keutschite associated with CalciteCaCO3
1 photo of Keutschite associated with 'Bournonite-Seligmannite Series'
1 photo of Keutschite associated with Tetrahedrite GroupM2(A6)M1(B4 C2)X3(D4)S1(Y12)S2(Z)
1 photo of Keutschite associated with LuzoniteCu3AsS4
1 photo of Keutschite associated with Tetrahedrite SubgroupCu6(Cu4C2+2)Sb4S12S
1 photo of Keutschite associated with ChalcopyriteCuFeS2

Related Minerals - Strunz-mindat GroupingHide

2.KA.05EnargiteCu3AsS4Orth. mm2 : Pmn21
2.KA.05Petrukite(Cu,Fe,Zn,Ag)3(Sn,In)S4Orth. mm2 : Pmn21
2.KA.10BriartiteCu2FeGeS4Tet.
2.KA.10PermingeatiteCu3SbSe4Tet. 42m : I42m
2.KA.10LuzoniteCu3AsS4Tet. 42m : I42m
2.KA.10BarquilliteCu2CdGeS4Tet. 42m : I42m
2.KA.10FamatiniteCu3SbS4Tet. 42m : I42m
2.KA.10ZincobriartiteCu2(Zn,Fe)(Ge,Ga)S4Tet. 42m : I42m
2.KA.15FangiteTl3AsS4Orth. mmm(2/m2/m2/m) : Pnma

Fluorescence of KeutschiteHide

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Internet Links for KeutschiteHide

References for KeutschiteHide

Localities for KeutschiteHide

Showing 3 localities.

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.
Germany
 
  • Baden-Württemberg
    • Freiburg Region
      • Ortenaukreis
        • Oberwolfach
Kolitsch et al. (2019)
Peru (TL)
 
  • Lima
    • Oyón Province
      • Oyón District
        • Uchucchacua area
Williams et al. (2014) +2 other references
Romania
 
  • Hunedoara County
    • Certeju de Sus
Dincă et al. (2025)
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