The Lengenbach Quarry in Switzerland: Classic Locality for Rare Thallium Sulfosalts

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Review Article

Author(s): Raber, Thomas; Roth, Philippe

Publication Date: 2018-09

Permanent Link: https://doi.org/10.3929/ethz-b-000302136

Originally published in: Minerals 8(9), http://doi.org/10.3390/min8090409

Rights / License: Creative Commons Attribution 4.0 International

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Review The Lengenbach Quarry in Switzerland: Classic Locality for Rare Thallium Sulfosalts †

Thomas Raber 1,* and Philippe Roth 1,2

1 Lengenbach Research Association (Forschungsgemeinschaft Lengenbach, FGL), Gemeinde Binn, Dorfstr. 11, 3996 Binn, Switzerland 2 Swiss Seismological Service, ETH Zurich, Sonneggstr. 5, 8092 Zurich, Switzerland; [email protected] * Correspondence: [email protected] † Anniversary publication—60 years of continuous mineral search at Lengenbach and 15 years of FGL.

Received: 11 July 2018; Accepted: 6 September 2018; Published: 14 September 2018

Abstract: The Lengenbach quarry is a world-famous mineral locality, especially known for its rare and well-crystallized Tl, Pb, Ag, and Cu bearing sulfosalts. As of June 2018, it is the type locality for 44 different mineral species, making it one of the most proliﬁc localities worldwide. A total of 33 thallium mineral species have been identiﬁed, 23 of which are type minerals. A brief description of several thallium species of special interest follows a concise and general overview of the thallium mineralization.

Keywords: Lengenbach; Binn valley; thallium; sulfosalts; hutchinsonite; fangite; richardsollyite; sartorite; routhierite-stalderite; chabournéite-dalnegroite

1. Introduction The Lengenbach quarry in the Binn valley, Valais, Switzerland (Figures1 and2) is located in Triassic meta-dolomites of the Penninic zone in the Swiss Alps. Metal extraction for economic purposes never occurred in the quarry, but specimen extraction has been continuously carried out since 1958. The quarry is currently operated by the Forschungsgemeinschaft Lengenbach (FGL, literally: Lengenbach Research Association), financed by a group of idealistic collectors and by the local community of Binn. The purpose of the research association is to promote scientific research on the unique minerals of the Lengenbach deposit and of other dolomite localities in the Binn valley. An intermittent, measured specimen extraction during the snow-free summer months shall guarantee the potential for scientific investigations on the one hand and deliver dolomite material for a publicly accessible dump, serving as an attraction to equally eager tourists and mineral collectors, on the other hand. This brief review gives a glimpse at the current status of the mineralogical research with regard to the thallium mineralization at the locality. For further information about history, geology, and mineral extracting work we recommend References [1,2].

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Figure 1. The upper part of the Lengenbach quarry in the Binn valley, view to the east. FigureFigure 1. 1.The The upper upper part part ofof thethe LengenbachLengenbach quarry quarry in in the the Binn Binn valley, valley, view view to tothe the east. east.

Figure 2. Ralph Cannon, technical head of the Forschungsgemeinschaft Lengenbach (FGL) research Figure 2. Ralph Cannon, technical head of the Forschungsgemeinschaft Lengenbach (FGL) research Figureassociation, 2. Ralph at Cannon, the entrance technical of the head quarry of the in Forschungsgemeinschaft front of the concrete Lengenbach hall, where (FGL) the current research association, at the entrance of the quarry in front of the concrete hall, where the current association,mineral-extraction at the entrance activities of the are quarry carried in out front at the of thelowest concrete dolomite hall, level. where the current mineral-extraction mineral-extraction activities are carried out at the lowest dolomite level. activities are carried out at the lowest dolomite level. 2. Geochemical Setting and Formation of the Lengenbach Locality 2. Geochemical2. Geochemical Setting Setting and and Formation Formation ofof thethe Lengenbach Locality Locality The Lengenbach ore body is located within the Penninic Monte Leone nappe, at the Northern The Lengenbach ore body is located within the Penninic Monte Leone nappe, at the Northern frontThe and Lengenbach subvertical ore hinge body zone is located of a large within fold. the The Penninic stratabound Monte mineralization Leone nappe, occursat the Northern in the front and subvertical hinge zone of a large fold. The stratabound mineralization occurs in the frontstrati andgraphically subvertical uppermost hinge zonepart of of the a 240 large m thick fold. dolomite The stratabound sequence. mineralization occurs in the stratigraphically uppermost part of the 240 m thick dolomite sequence. stratigraphicallyThe formation uppermost of the part highly of the complex 240 m mineralization thick dolomite in sequence. the Lengenbach deposit is not yet The formation of the highly complex mineralization in the Lengenbach deposit is not yet completelyThe formation understood. of the While highly Graeser complex [3] suggested mineralization a late introduction in the Lengenbach of As, Tl, deposit and Cu is into not a yet completely understood. While Graeser [3] suggested a late introduction of As, Tl, and Cu into a completelypre-existing understood. Fe-Pb-Zn mineralization While Graeser during [3] suggested Alpine metamorphism a late introduction from the of underlying As, Tl, and gneissic Cu into pre-existing Fe-Pb-Zn mineralization during Alpine metamorphism from the underlying gneissic basement, Hofmann and Knill [4] proposed a pre-Alpine origin of those elements and a subsequent a pre-existingbasement, Hofmann Fe-Pb-Zn and mineralization Knill [4] proposed during a pre Alpine-Alpine metamorphism origin of those fromelements the underlyingand a subsequent gneissic isochemical Alpine metamorphism, under upper greenschist to lower amphibolite facies. isochemical Alpine metamorphism, under upper greenschist to lower amphibolite facies.

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basement,Minerals 2018 Hofmann, 8, x FOR PEER and REVIEW Knill [4 ] proposed a pre-Alpine origin of those elements and a subsequent3 of 16 isochemical Alpine metamorphism, under upper greenschist to lower amphibolite facies. AccordingAccording to to Hofmann Hofmann and and Knill Knill [4 ],[4], the the distinct distinct mineral mineral associations associations in in the the different different parts parts ofof the Lengenbachthe Lengenbach dolomite dolomite can be can understood be understood as a result as a of result slow of crystallization slow crystallization processes processes in two in different two redoxdifferent environments. redox environments. One is based Oneon graphite is based and/or on graphi pyrite–pyrrhotite,te and/or pyrite leading–pyrrhotite, to zerovalent leading arsenic. to Thezerovalent other, which arsenic. was essentialThe other, for which the rarewas sulfosalts’essential for formation, the rare sulfosalts’ is controlled formation, by baryte is controlled (sulfate)–pyrite by baryte (sulfate)–pyrite (sulfide), leading to trivalent arsenic. Accordingly, the As(III)-rich zone in the (sulﬁde), leading to trivalent arsenic. Accordingly, the As(III)-rich zone in the central part of the quarry central part of the quarry shows an enrichment in baryte and hosts the coveted Tl-Pb-Ag-Cu bearing shows an enrichment in baryte and hosts the coveted Tl-Pb-Ag-Cu bearing sulfosalts. sulfosalts. Graeser [3] as well as Hofmann and Knill [4] have each proposed a zonation scheme for the Graeser [3] as well as Hofmann and Knill [4] have each proposed a zonation scheme for the differentdifferent types types of mineralof mineral assemblages. assemblages. While While the the former former considers considers in in essence essence only only mineralogical mineralogical and spatialand criteria, spatial criteria, the later the rely later on rely geochemistry on geochemistry and there and is there no obvious is no obvious link between link between the two the zonations. two However,zonations. it is However, clear that it the is Tl-richclear that zone the is Tl restricted-rich zone to is the restricted central partto the of thecentral quarry. part Whileof the onquarry. a broad scaleWhile the different on a broad bedding-parallel scale the different zones bedding containing-parallel the zones different containing assemblages the different strike subverticallyassemblages in anstrike east–west subvertically direction in (Figure an east1),– onwest the direction more local (Figure scale, 1) they, on can the be more subdivided local scale, into they ribbons can be and ellipsoidalsubdivided lenses into that ribbons thicken, and toellipsoidal a maximum lenses thickness that thicken, of 0.5 to m, a andmaximum pinch out.thickness of 0.5 m, and pinchThe out. FGL has been working for a few years on three such ribbons in the Tl-rich central zone (Figure3The). TheyFGL has are been spaced working approximately for a few years 1 m apart,on three measure such ribbons a maximum in the Tl of-rich 4 mcentral× 2 zone m and are(Figure designated, 3). They from are northspaced to approximately south as ribbons 1 m 1,apart, 1/2, measure and 2. a Structurally, maximum of they 4 m are× 2 ellipsoidalm and are in shape,designated, with a sharpfrom north contact to south to the as surrounding, ribbons 1, 1/2, mineral-poor and 2. Structurally, dolomite. they Theare ellipsoidal contrast is in essentially shape, a mineralogical-geochemical,with a sharp contact to the not surrounding, a lithological mineral contrast.-poor dolomite. Thanks to The their contrast high is realgar essentially contents, a allmineralogical three ribbons-geochemical, are easily identiﬁed not a lithological in situ. contrast. But while Thanks ribbon to their 1 is high very realgar rich incontents, thallium all thre species,e ribbons are easily identified in situ. But while ribbon 1 is very rich in thallium species, the very the very brittle and orpiment-rich dolomite of ribbon 1/2 is poorer in Tl while the realgar-richest brittle and orpiment-rich dolomite of ribbon 1/2 is poorer in Tl while the realgar-richest ribbon 2 is ribbon 2 is almost bare of any thallium-species. Table1 summarizes all species found in ribbon 1; almost bare of any thallium-species. Table 1 summarizes all species found in ribbon 1; 18 species 18 species containing thallium as one of main constituents are marked in bold characters. containing thallium as one of main constituents are marked in bold characters.

FigureFigure 3. 3.Three Three realgar-rich realgar-rich ribbons ribbons in in the central dolomite dolomite zone zone in in the the lower lower part part of ofthethe quarry. quarry. RibbonRibbon 1 (red) 1 (red) is very is very rich rich in thallium in thallium species, species, ribbon ribbon 1/2 1/2(yellow) (yellow) contains contains much much orpiment orpiment in a in brittle a brittle dolomite and is poorer in thallium, ribbon 2 (orange) is the realgar-richest ribbon, but almost dolomite and is poorer in thallium, ribbon 2 (orange) is the realgar-richest ribbon, but almost bare of bare of any thallium species. The maximum ribbon thickness is about 0.5 m. Dashed lines show the any thallium species. The maximum ribbon thickness is about 0.5 m. Dashed lines show the expected expected extension of the ribbons below the debris. extension of the ribbons below the debris.

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Table 1. Species constituting the mineral assemblage of ribbon 1 in the Lengenbach quarry. Tl minerals are marked in bold, modiﬁed after reference [5].

“Adularia” and “hyalophane” Hutchinsonite Rathite Aktashite Hydrocerussite Realgar Argentobaumhauerite Incomsartorite Richardsollyite Argentodufrénoysite Imhofite Routhierite Argentoliveingite Jentschite Rutile Arsenic Jordanite Sartorite Baryte Kaolinite Seligmannite Baumhauerite Lengenbachite Silver Bernardite Liveingite Sinnerite Canfieldite (Te-rich) Marrite Smithite Cerussite Muscovite Sphalerite Coffinite Nowackiite Stalderite Covellite Orpiment Tennantite Dolomite Pararealgar Thalcusite Dravite Parapierrotite Thorite Dufrénoysite Picotpaulite Tochilinite Edenharterite Proustite Trechmannite Erniggliite Pyrite Uraninite Ferrostalderite Quadratite Wallisite Galena Quartz Wurtzite Hatchite Ralphcannonite Xanthoconite

3. Overview of Thallium Minerals at Lengenbach As of June 2018, the Lengenbach quarry hosts 160 different mineral species, with sulﬁdes and sulfosalts being the major group representing 57% of these species (Table2 and Figure4). Forty-four minerals are so called type minerals as they have been found and described for the ﬁrst time from this locality. Twenty-three of them are thallium minerals. Table3 lists all known Lengenbach thallium minerals as of today.

Table 2. Mineralogical overview of the Lengenbach quarry.

Category Number Mineral species * 160 Elements 6 Sulﬁdes and sulfosalts 91 Chalcogenides 2 Carbonates 10 Sulfates and molybdates 10 Phosphates and arsenates 8 Oxides 13 Silicates 20 Type minerals 44 Thallium minerals 33 * IMA (International Mineralogical Association) approved. Minerals 2018, 8, 409 5 of 17 Minerals 2018, 8, x FOR PEER REVIEW 5 of 16

Silicates Elements 13% 4% Oxides 8%

Phosphates & arsenates 5% Sulfides & Sulfates & molybdates sulfosalts 6% 57% Carbonates 6% Chalcogenids 1%

Figure 4. Distribution of mineral classes at Lengenbach. Figure 4. Distribution of mineral classes at Lengenbach. Table 3. Thallium minerals at Lengenbach.

TableYear 3. of Thallium First Description minerals at Lengenbach.Reference for the Occurrence Mineral Species Chemical Formula from Lengenbach at Lengenbach Year of First Description Reference for the Occurrence Mineral Species Chemical Formula Bernardite Tl(As,Sb)5S8 1992from Lengenbach Graeser (in Hofmannat et Lengenbach al.) [6] Chabournéite Tl4Pb2(Sb,As)20S34 2017 Roth [7] Bernardite Tl(As,Sb)5S8 1992 Graeser (in Hofmann et al.) [6] Dalnegroite * Tl4Pb2(As,Sb)20S34 2009 Nestola et al. [8] Chabournéite Tl4Pb2(Sb,As)20S34 2017 Roth [7] Dekatriasartorite * TlPb58As97S204 2017 Topa et al. [9] Edenharterite *Dalnegroite TlPbAs * 3S6 Tl4Pb2(As,Sb)20S34 19922009 Graeser & SchwanderNestola [10] et al. [8] EnneasartoriteDekatriasartorite * Tl6Pb32 *As 70S140TlPb58As97S204 20172017 Topa et al. [11Topa] et al. [9] Erniggliite *Edenharterite Tl2 *SnAs 2S6 TlPbAs3S6 19921992 GraeserGraeser et al. [12 &] Schwander [10] Fangite Tl3AsS4 2017 Roth [13] Enneasartorite * Tl6Pb32As70S140 2017 Topa et al. [11] Ferrostalderite * CuFe2TlAs2S6 2016 Biagioni et al. [14] Erniggliite * Tl2SnAs2S6 1992 Graeser et al. [12] Gabrielite * Tl2AgCu2As3S7 2006 Graeser et al. [15] 3 4 Hatchite *Fangite AgTlPbAs 2S5 Tl AsS 19122017 Solly & Smith [16Roth] [13] HendekasartoriteFerrostalderite * Tl2Pb 48* As82S172CuFe2TlAs2S6 20172016 Topa et al.Biagioni [11] et al. [14] Heptasartorite *Gabrielite Tl7 Pb* 22As55S108Tl2AgCu2As3S7 20172006 Topa et al. [Graeser11] et al. [15] Hutchinsonite * TlPbAs S 1905 Solly [17] Hatchite * 5 9 AgTlPbAs2S5 1912 Solly & Smith [16] Imhoﬁte * Tl5.6As15S25.3 1965 Burri et al. [18] Hendekasartorite * Tl2Pb48As82S172 2017 Topa et al. [11] Incomsartorite * Tl6Pb144As246S516 2016 Topa et al. [19] Heptasartorite * Tl7Pb22As55S108 2017 Topa et al. [11] Jentschite * TlPbAs2SbS6 1997 Graeser & Edenharter [20] LoránditeHutchinsonite TlAsS* 2 TlPbAs5S9 19671905 Graeser [21] Solly [17] ParapierrotiteImhofite Tl(Sb,As)* 5S8 Tl5.6As15S25.3 20161965 Raber [22]Burri et al. [18] Philrothite *Incomsartorite TlAs * 3S5 Tl6Pb144As246S516 20142016 Bindi et al. [23Topa] et al. [19] Picotpaulite TlFe2S3 2015 Roth [24] Jentschite * TlPbAs2SbS6 1997 Graeser & Edenharter [20] Raberite * Tl5Ag4As6SbS15 2012 Bindi et al. [25] Lorándite TlAsS2 1967 Graeser [21] Raguinite TlFeS2 2017 Roth [26] Parapierrotite Tl(Sb,As)5S8 2016 Raber [22] Ralphcannonite * AgZn2TlAs2S6 2015 Bindi et al. [27] Rathite * PhilrothiteAg2Pb 12-x* Tlx/2As18+x/2TlAsS40 3S5 18962014 Baumhauer [28Bindi] et al. [23] Richardsollyite *Picotpaulite TlPbAsS 3 TlFe2S3 20172015 Meisser et al. [5]Roth [24] Routhierite CuHg TlAs S 2016 Roth [29] Raberite * 2 2 6Tl5Ag4As6SbS15 2012 Bindi et al. [25] Sicherite * TlAg2(As,Sb)3S6 2001 Graeser et al. [30] Raguinite TlFeS2 2017 Roth [26] Spaltiite * Tl2Cu2As2S5 2014 Graeser et al. [31] Ralphcannonite * AgZn2TlAs2S6 2015 Bindi et al. [27] Stalderite * CuZn2TlAs2S6 1995 Graeser et al. [32] ThalcusiteRathite * Tl 2Cu3FeSAg4 2Pb12-xTlx/2As18+x/2S40 20051896 Cannon [33Baumhauer] [28] Wallisite *Richardsollyite CuTlPbAs * 2S5 TlPbAsS3 19652017 Nowacki [34Meisser] et al. [5] WeissbergiteRouthierite TlSbS2 CuHg2TlAs2S6 20142016 Raber & Roth [35Roth] [29] Sicherite * * Type mineralsTlAg2(As,Sb) from the3S6 Lengenbach quarry.2001 Graeser et al. [30] Spaltiite * Tl2Cu2As2S5 2014 Graeser et al. [31] Stalderite * CuZn2TlAs2S6 1995 Graeser et al. [32] From the 73 validThalcusite mineral speciesTl2 containingCu3FeS4 essential thallium2005 worldwide (accordingCannon [33] to mindat.org [36]), the strikingWallisite * number ofCuTlPbAs 33 species2S5 (45.2%) could be1965 found at Lengenbach.Nowacki [34] Weissbergite TlSbS2 2014 Raber & Roth [35] 4. On Some Special Thallium Minerals from* Type theminerals Lengenbach from the Lengenbach Quarry quarry.

We focus here onFrom a few the thallium 73 valid species mineral of special species interest, containing as a discussion essential thallium of all thallium worldwide sulfosalts (according to would be beyondmindat.org the scope [36]), of this the briefstriking note. number of 33 species (45.2%) could be found at Lengenbach.

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4. On Some Special Thallium Minerals from the Lengenbach Quarry Minerals 2018, 8, 409 6 of 17 We focus here on a few thallium species of special interest, as a discussion of all thallium sulfosalts would be beyond the scope of this brief note. 4.1. Hutchinsonite—The First of Its Kind 4.1. Hutchinsonite—The First of Its Kind The first thallium mineral from Lengenbach, hutchinsonite, TlPbAs5S9, was found in 1903, when theThe English first thallium expert mineral of Lengenbach from Lengenbach, minerals, Richardhutchinsonite, Harrison TlPbAs Solly5S9, (1851–1925), was found induring 1903, when one of histhe many English trips expert to this of remote Lengenbach Binn valley,minerals, recognized Richard Harrison that the Solly red to (1851 greyish-black,–1925), during often one flattened of his orthorhombicmany trips crystals to this remoteprobably Binn were valley, belonging recognized to a new that species. the red He to briefly greyish described-black, often it in flattened 1904 [37 ], withoutorthorhombic giving it crystals a name. probably In 1905, we hisre colleague belonging atto thea new British species. Museum, He briefly G.T. described Prior was it in able 1904 to [37], reveal thewithout presence giving of 20 it wt a %name. Tl in In hutchinsonite. 1905, his colleague This at was the of British “especial Museum, interest”, G.T. Prior as Solly was [ 17able] wrote to reveal in his followingthe presence detailed of 20 description, wt % Tl in hutchinsonite. in which he named This was the of mineral “especial after interest”, Arthur as Hutchinson Solly [17] wrote (1866–1937). in his Prior’sfollowing discovery detailed of description, thallium in in hutchinsonite which he named was the important mineral after enough Arthur to Hutchinson result in a (1866 short–1937). note in NaturePrior’s[38 ], discovery as it was of only thallium the third in hutchinsonite mineral worldwide was important (after crookesiteenough to result and lor iná ndite) a short to note contain in Nature [38], as it was only the third mineral worldwide (after crookesite and lorándite) to contain thallium as an essential constituent. thallium as an essential constituent. Hutchinsonite is the most common thallium species in the deposit and represents the type Hutchinsonite is the most common thallium species in the deposit and represents the type structure of a family of complex sulfosalts. Its crystals are commonly transparent and prismatic, due to structure of a family of complex sulfosalts. Its crystals are commonly transparent and prismatic, due c an elongationto an elongation parallel parallelto the axis to (seethe Figuresc axis (see5–7), Figures or, rarely, 5– more7), or, or lessrarely, isometric. more or Hutchinsonite less isometric. may containHutchinsonite antimony may that contain contributes antimony the crystals that contributes to be darker the crystals and opaque. to be darker The two and varieties, opaque. The prismatic two Sb-freevarieties, and moreprismatic isometric Sb-free Sb-bearing and more isometric hutchinsonites, Sb-bearing may hutchinsonites, be closely associated. may be closely The crystals associated. reach 2 mmThe in crystals size. reach 2 mm in size.

FigureFigure 5. Dark5. Dark wine-red, wine-red,transparent, transparent, lath lath-like-like hutchinsonite hutchinsonite crystals crystals on ondolomite. dolomite. FieldField of view of 1.4 view 1.4 mm.mm. Photo: Edgar Edgar Müller. Müller.

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FigureFigureFigure 6. 6.Translucent6. TranslucentTranslucent aggregate aggregate of ofparallel of parallel parallel-oriented,-oriented,-oriented, red, red, flattened red, flattened ﬂattened hutchinsonite hutchinsonite hutchinsonite crystals crystals crystals with with pyrite withpyrite pyrite ononon dolomite. dolomite. dolomite. Field Field of ofview: view: view: 2.5 2.5 2.5mm. mm. mm. Photo: Photo: Photo: Stephan Stephan Stephan Wolfsried. Wolfsried. Wolfsried.

Figure 7. Prismatic dark-red to grey crystals of hutchinsonite. Field of view: 1.5 mm. Photo: Stephan FigureFigure 7. 7.PrismaticPrismatic dark- dark-redred to grey to crystals grey crystals of hutchinsonite of hutchinsonite.. Field of view: Field 1.5 ofmm. view: Photo: 1.5 Stephan mm. Photo: Wolfsried. Wolfsried.Stephan Wolfsried.

4.2.4.2.4.2. Fangite Fangite—The Fangite——TheThe Thallium Thallium-RichestThallium-Richest-Richest

Well-developed crystals of fangite, Tl3AsS4, could recently be identified for the first time WellWell-developed-developed crystals crystals of fangite, of fangite, Tl3AsS Tl4,3 AsS could4, recently could recently be identified be identified for the first for time the first [13]—to our knowledge, the first microscopically visible crystals of this species worldwide. They are [13]time—to [13 our]—to knowledge, our knowledge, the first microscopically the first microscopically visible crystals visible of this crystals species ofworldwide. this species They worldwide. are small, deep red, and very shiny (Figure 8). With more than 75 wt % Tl, fangite is the thallium-richest small,They deep are small,red, and deep very red, shiny and (Figure very 8). shiny With (Figuremore than8). 75 With wt % more Tl, fangite than 75is the wt thallium % Tl, fangite-richest is the mineral discovered at Lengenbach up to now. mineralthallium-richest discovered mineral at Lengenbach discovered up to at now. Lengenbach up to now. A Amorphological morphological study study of ofthe the small small crystals crystals [26] [26] showed showed them them to todisplay display different different com combinationsbinations A morphological study of the small crystals [26] showed them to display different combinations of ofcrystal crystal forms, forms, irrespective irrespective of ofthe the fact fact that that the the prismatic prismatic habit habit is isalways always approximately approximately the the same same of crystal forms, irrespective of the fact that the prismatic habit is always approximately the same (Figure(Figure 9). 9). (Figure9).

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FigureFigureFigure 8. 8.8. Tiny, Tiny,Tiny, prismatic,prismatic,prismatic, lustrous, lustrous, redred red fangitefangite fangite crystalscrystals crystals onon on dolomite.dolomite. dolomite. FieldField Field ofof view:view: of view: 0.750.75 0.75mm.mm. mm. Photo:Photo: Photo: MischaMischaMischa Crumbach. Crumbach.Crumbach.

Figure 9. Fangite crystals showing different combinations of forms but similar habits. A distinct FigureFigure 9. 9.Fangite Fangite crystals crystals showing showing different different combinations combinations of of forms forms but but similar similar habits. habits. A A distinct distinct color color is assigned to each crystal form. The Miller indices of the different forms are given without iscolor assigned is assigned to each to crystal each crystal form. form. The Miller The Miller indices indices of the of different the different forms forms are given are given without without brackets brackets FACES drawings [39]. FACESbrackets drawings FACES drawings [39]. [39].

4.3.4.3.4.3. Richardsollyite—Honoring RichardsollyiteRichardsollyite——HonoringHonoring aa a PioneePionee Pioneerrr InInIn 2015, 2015, 2015, the the the FGL FGL FGL extracted extracted extracted two two two specimens specimens specimens with with with an unknown an an unknown unknown mineral mineral mineral from from from the very the the very veryTl-rich Tl Tl-- dolomiterichrich dolomite ribbon 1 (Figure 3) in the center of the quarry. Its chemistry, as first determined by Energy ribbondolomite 1 (Figure ribbon3 1) in(Figure the center 3) in the of thecenter quarry. of the Its quarry. chemistry, Its chemistry, as ﬁrst determined as first determined by Energy by Energy Dispersive Dispersive X-ray Spectroscopy (EDXS) measurements in two independent institutes, showed the X-rayDispersive Spectroscopy X-ray Spectroscopy (EDXS) measurements (EDXS) measurements in two independent in two indepen institutes,dent showed institutes, the showed presence the of Tl, presence of Tl, Pb, As, and S in a simple, yet unknown ratio of 1:1:1:3. Also the powder X-ray Pb,presence As, and of S Tl, in a Pb, simple, As, and yet Sunknown in a simple, ratio yet of 1:1:1:3. unknown Also ratio the of powder 1:1:1:3. X-ray Also diagram the powder did Xnot-ray match diagram did not match with any known listed natural or synthetic chemical compound in the withdiagram any known did not listed match natural with any or synthetic known listed chemical natural compound or synthetic in the chemical relevant compound databases. in One the year relevantrelevant databases.databases. OneOne yearyear later,later, MeisserMeisser etet al.al. [5][5] couldcould describedescribe thisthis mineralmineral asas aa newnew speciesspecies withwith later, Meisser et al. [5] could describe this mineral as a new species with the name richardsollyite 3 thethe namename richardsollyiterichardsollyite (Figure(Figure 10),10), TlPbAsSTlPbAsS3,, honoringhonoring thethe aforementionedaforementioned pioneerpioneer ofof LengenbachLengenbach (Figure 10), TlPbAsS , honoring the aforementioned pioneer of Lengenbach investigations at the dawn investigationsinvestigations at at the the3 dawn dawn of of the the twentieth twentieth century, century, R.H. R.H. Solly. Solly. The The crystal crystal structure structure of of of the twentieth century, R.H. Solly. The crystal structure of richardsollyite is new in nature, being richarrichardsollyitedsollyite isis newnew inin nature,nature, beingbeing previouslypreviously knownknown onlyonly inin somesome syntheticsynthetic alkalialkali sulfosaltssulfosalts [5].[5]. previously known only in some synthetic alkali sulfosalts [5].

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FigureFigure 10. 10. HolotypeHolotype specimen specimen of of richardsollyite richardsollyite (dark (dark grey) grey) with hutchinsonite (dark red) and and realgar. realgar. Field of view: 3.5 mm. Mineralogical Collection of the Musée cantonal de géologie (MGL no. Field of view: 3.5 mm. Mineralogical Collection of the Musée cantonal de géologie (MGL no. 080126), 080126), photo: Stefan Ansermet. photo: Stefan Ansermet.

4.4.4.4. The The New New “Sartorites “Sartorites”—From”—From a Species a Species to a toGroup a Group

Sartorite, PbAs2S4, was first described by vom Rath as “scleroclase” in 1864 [40], and shortly Sartorite, PbAs2S4, was first described by vom Rath as “scleroclase” in 1864 [40], and shortly after afterrenamed renamed by by Dana Dana [41 [41]] to to honor honor Wolfgang Wolfgang SartoriusSartorius von von Waltershausen Waltershausen (1809 (1809–1876),–1876), a professor a professor of of mineralogy in Göttingen, Germany. In 1919, Smith and Solly [42] recognized that sartorite mineralogy in Göttingen, Germany. In 1919, Smith and Solly [42] recognized that sartorite has—despite has—despite its simple chemical formula—a quite unique and complex crystal structure: “sartorite its simple chemical formula—a quite unique and complex crystal structure: “sartorite appears to rank appears to rank with the telluride of gold, calaverite, in the peculiarity of its atomic arrangement, since in with the telluride of gold, calaverite, in the peculiarity of its atomic arrangement, since in certain at least of his certain at least of his crystals there exist simultaneously two or even three incongruent space-lattices, which maycrystals be supposed there exist derivable simultaneously from one another two or evenby a slight three incongruentshear.” It is quite space-lattices, remarkable which that may they be supposedwere able, derivable withfrom the one limited another bymethods a slight of shear their.” It time is quite—in essenceremarkable only that crystal they-morphological were able, with investigations the limited methods—to of recognizetheir time—in the so essence-called componly crystal-morphologicallex and incommensurate investigations—to nature of both the recognize calaverite the and, so-called partly, complex sartoriteand incommensurate structures. nature of both the calaverite and, partly, sartorite structures. AfterAfter the the introduction introduction of ofX-ray X-ray investigations investigations in crystallography, in crystallography, several several different different monoclinic monoclinic supersuper cells (superstructures) (superstructures) were were described described [43 – [4346–].46]. Berlepsch Berlepsch et al. et [46 al.] pointed [46] pointed to the crystallographic to the crystallographicconsequences of consequences the complex of correlated the complex atomic correlated substitution atomic by substitution which substantial by which amounts substantial of thallium amountsare incorporated of thallium into are the incorporated sartorite structure. into the They sartorite found structure. a so-called They 9-fold found superstructure a so-called for 9-fold a sartorite superstructurewith up to 6.5 for wt a sartorite % Tl and with discussed up to 6.5 wt this % asTl and a “lock-in” discussed structure this as a “lock with-in” acommensurate structure with a lattice, commensuratefor a species that lattice, they for regarded a species asthat usually they regarded incommensurate. as usually incommensurate. TheThe true true nature nature of ofsartorite sartorite was was finally finally resolved resolved by Topa by Topa et al. et[9,11,19]. al. [9,11 Based,19]. Basedon a systematic on a systematic combinationcombination of of electron microprobe measurements measurements and and crystal crystal structure structure determinations determinations they they showed showed that “sartorite” actually represents a group of different mineral species with distinct crystal that “sartorite” actually represents a group of different mineral species with distinct crystal structures structures and distinct chemical compositions. According to their different superstructures, the new and distinct chemical compositions. According to their different superstructures, the new “sartorites” “sartorites” were named by adding a Greek prefix, which corresponds to an integral multiple of the were named by adding a Greek prefix, which corresponds to an integral multiple of the basic “sartorite” basic “sartorite” substructure with 4.2 Å (Table 4). substructure with 4.2 Å (Table4).

Minerals 2018, 8, 409 10 of 17

Minerals 2018, 8, x FOR PEER REVIEW 10 of 16 Table 4. The new sartorite minerals. Table 4. The new sartorite minerals. Mineral Name Chemical Formula Superstructure of the Sartorite Subcell (4.2 Å) Mineral Name Chemical Formula Superstructure of the Sartorite Subcell (4.2 Å) Heptasartorite [11] Tl7Pb22As55S108 7-fold Heptasartorite [11] Tl7Pb22As55S108 7-fold Enneasartorite [11] Tl6Pb32As70S140 9-fold EnneasartoriteHendekasartorite [11] [11 ]Tl Tl6Pb2Pb3248AsAs70S82140S172 911-fold-fold HendekasartoriteIncomsartorite [19[11]] Tl Tl26PbPb48144AsAs82S246172S 516 11-fold (incommensurate)11-fold IncomsartoriteDekatriasartorite [19] [9 ]Tl6 TlPbPb14458AsAs24697SS516204 11-fold (incommensurate)13-fold Dekatriasartorite [9] TlPb58As97S204 13-fold These species are not visually distinguishable. The crystals are lead-grey with a metallic luster. These species are not visually distinguishable. The crystals are lead-grey with a metallic luster. Well-developed crystals show a prismatic habit with more or less distinct striation parallel to the Well-developed crystals show a prismatic habit with more or less distinct striation parallel to the longitudinal axis (Figure 11). Their length reaches several centimeters. longitudinal axis (Figure 11). Their length reaches several centimeters.

FigureFigure 11. 11.Lead-grey, Lead-grey, metallic, metallic, prismatic prismatic crystalcrystal ofof dekatriasartorite.dekatriasartorite. Field Field of of view view 4.8 4.8 mm. mm. Photo: Photo: MischaMischa Crumbach. Crumbach.

4.5.4.5. The The Routhierite-Stalderite Routhierite-Stalderite Group—Complex Group—Complex SubstitutionsSubstitutions TheThe routhierite-stalderite routhierite-stalderite series series is is a a group group of thallium arsenio arsenio-sulfosalts-sulfosalts with, with, in in addition, addition, monovalentmonovalent (Me1: (Me1: CuCu++, Ag Ag++) )and and bivalent bivalent metal metal ions ions (Me2: (Me2: Hg2+, Zn Hg2+2+, Fe, Zn2+) 2+and, Fe the2+ )generic and the formula generic TlMe1+Me22+As+ 2S6. 2+Accordingly, six different combinations, and thus six distinct mineral species are formula TlMe1 Me2 As2S6. Accordingly, six different combinations, and thus six distinct mineral speciestheoretically are theoretically possible in possible this group in this (Table group 5, Figure(Table 5 12)., Figure Five 12 could). Five indeed could be indeed found be in nature:found in arsiccioite, routhierite, stalderite, ralphcannonite, and ferrostalderite. The latter four occur in the nature: arsiccioite, routhierite, stalderite, ralphcannonite, and ferrostalderite. The latter four occur Lengenbach quarry, the type-locality for the latter three. Routhierite and arsiccioite are red to in the Lengenbach quarry, the type-locality for the latter three. Routhierite and arsiccioite are red dark-red in color, the other three are dark grey with a metallic luster, but they all show the same to dark-red in color, the other three are dark grey with a metallic luster, but they all show the same pseudo-cubic to prismatic morphology (≤1 mm). pseudo-cubic to prismatic morphology (≤1 mm).

Minerals 2018, 8, 409 11 of 17

Minerals 2018, 8, x FOR PEER REVIEW 11 of 16 Table 5. Routhierite-stalderite group minerals. Table 5. Routhierite-stalderite group minerals. Mineral Species Chemical Formula Mineral Species Chemical Formula Routhierite TlCuHg2As2S6 Routhierite TlCuHg2As2S6 Stalderite TlCuZn2As2S6 Stalderite TlCuZn2As2S6 Ferrostalderite TlCuFe2As2S6 Ferrostalderite TlCuFe2As2S6 Ralphcannonite TlAgZn2As2S6 Ralphcannonite TlAgZn2As2S6 Arsiccioite TlAgHg2As2S6 Arsiccioite TlAgHg2As2S6 Unknown TlAgFe2As2S6 Unknown TlAgFe2As2S6

FigureFigure 12. The 12. The minerals minerals of the of routhierite-stalderite the routhierite-stalderite group group in a blockin a block diagram. diagram. The six The distinct six distinct species arespecies the result are of the the result six possible of the six combinations possible combinations of monovalent of monovalent (Ag+, Cu+ )(Ag and+, Cu bivalent+) and metalbivalent ions metal (Zn 2+, 2+ 2+ 2+ Hg2+ions, Fe (Zn2+)., Modiﬁed Hg , Fe after). Modified Reference after [Reference27]. [27].

In theIn framethe frame of a series of a series of EDXS of EDXS analyses analyses on Lengenbach on Lengenbach samples samples from the from mineralogical the mineralogical collection of thecollection Eidgenössiche of the Eidgenössiche Technische Hochschule Technische (ETH) Hochschule collection (ETH) in Zurich, collection we recently in Zurich, identiﬁed we recently what to ouridentified knowledge what are the to our ﬁrst knowledge completely are idiomorphic the first completely crystals of routhierite idiomorphic worldwide crystals of (Figure routhierite 13). worldwide (Figure 13). Arsiccioite has not yet been found at Lengenbach. However, a single EDXS analysis of a minute Arsiccioite has not yet been found at Lengenbach. However, a single EDXS analysis of a minute crystal indicated a possible dominance of silver and iron, and thus, the possible existence of the last crystal indicated a possible dominance of silver and iron, and thus, the possible existence of the last unreported member of this group in the quarry. unreported member of this group in the quarry.

Minerals 2018, 8, 409 12 of 17 Minerals 2018, 8, x FOR PEER REVIEW 12 of 16 Minerals 2018, 8, x FOR PEER REVIEW 12 of 16

FigureFigure 13. 13.Idiomorphic, Idiomorphic, pseudo-cubic pseudo-cubic crystalscrystals of routhierite from from the the mineralogical mineralogical collection collection of the of the EidgenössicheEidgenössicheFigure 13. Idiomorphic, Technische Technische pseudo Hochschule Hochschule-cubic ETH crystalsETH inin Zurich.Zurich.of routhierite from the mineralogical collection of the Eidgenössiche Technische Hochschule ETH in Zurich. 4.6.4.6. Chabourn Chabournéiteéite-Dalnegroite—And-Dalnegroite—And Possibly Possibly MoreMore 4.6. Chabournéite-Dalnegroite—And Possibly More DalnegroiteDalnegroite was was described described as as a a new new mineral mineral species species from Lengenbach Lengenbach in in 2009 2009 [8]. [8 ]. It is It is consideredconsideredDalnegroite the the As-analogue As was-analogue described of of chabourn chabournéite. as a newéite. mineral The The latter latter species was was also from also recently recently Lengenbach identified identified in 2009 in in one [8]. one single It single is specimenspecimenconsidered showing showing the As what- whatanalogue appears of chabournéite. to to be be the the first first Thedistinct distinctlatter crystals was crystals also for the recently for species: the identified species: They are in Theyvery one similar aresingle very similartospecimen the to dalnegroite the showing dalnegroite crystalswhat appears crystalsand also to beandshow the also firsta strong showdistinct similarity a crystals strong to for similarity lengenbachite the species: to lengenbachiteTh crystals,ey are verywhich similar crystals, may whichimplyto the may dalnegroitethat imply the two that crystals rare the species two and rare alsomay speciesshow have abeen maystrong mistaken have similarity been for mistakenlengenbachiteto lengenbachite forlengenbachite in thecrystals, past (Figurewhich in the may 14). past (FigureBothimply 14 dalnegroite that). Boththe two dalnegroite and rare chabournéite species and may chabourn arehave Pb been-bearingéite mistaken are species. Pb-bearing for Inlengenbachite ribbon species. 1/2, however,inIn the ribbon past the 1/2,(Figure FGL however, 14). has Both dalnegroite and chabournéite are Pb-bearing species. In ribbon 1/2, however, the FGL has therecently FGL has found recently a few found samples a few of samples a Pb-free of dalnegroite a Pb-free dalnegroite (Figure 15), (Figure the equivalent 15), the equivalent of the Pb-free of the recently found a few samples of a Pb-free dalnegroite (Figure 15), the equivalent of the Pb-free Pb-freechabournéite chabourn froméite from Jas Roux,Jas Roux, France France [47,48]. [47 ,48 The]. The Pb-free Pb-free species species may may well well be be distinct distinct minerals minerals chabournéite from Jas Roux, France [47,48]. The Pb-free species may well be distinct minerals (Figure(Figure 16 ).16 Their). Their study study needs needs to to be be refined refined andand completed.completed. (Figure 16). Their study needs to be refined and completed.

Figure 14. Black, stellar aggregates of chabournéite on dolomite. Field of view 1.2 mm. Photo: M. FigureCrumbach.Figure 14. 14.Black, Black, stellarstellar aggregatesaggregates of of chabournéite chabournéite on on dolomite. dolomite. Field Field of view of view 1.2 mm. 1.2 mm.Photo: Photo:M. M.Crumbach. Crumbach.

Minerals 2018, 8, 409 13 of 17

Minerals 2018,, 8,, xx FORFOR PEERPEER REVIEWREVIEW 13 of 16

FigureFigure 15. 15.Aggregate Aggregate of of small small acicular acicular crystalscrystals of “Pb “Pb-free-free dalnegroite” dalnegroite” from from ribbon ribbon 1. 1.Field Field of view of view 0.60.6 mm. mm.

FigureFigure 16. 16.Diagram Diagram of Jas of Roux Jas and Roux Abuta and (France, Abuta resp. (France, Japan, resp. open Japan, diamonds) open chabourn diamonds)é ite, Montechabournéite,Monte Arsiccio (Italy, Arsiccio open circles) (Italy, protochabourn open circles) protochabournéiteéite and Lengenbach and Lengenbach (open squares) (open dalnegroite, squares) modiﬁeddalnegroite, after modified Reference after [48 ], Reference with copyright [48],, with with permission copyright copyright from pe permission Mineralogical from Mineralogical Association of Canada,Association 2013. of Dalnegroites Canada, 2013 are.. DalnegroitesDalnegroites located in the areareAs-dominated locatedlocated inin thethe AsAs left-dominated part of the left diagram, part of the chabourn diagram,éites chabournéites and protochabournéites in the right part with Sb-dominance. The Pb content andchabournéites protochabourn andéites protochabournéites in the right part with in Sb-dominance. the right part The with Pb Sb content-dominance. increases The along Pb content the y-axis. increases along the y-axis. The new Lengenbach samples (analyzed by EDXS) are shown as red Theincreases new Lengenbach along the samples y-axis. The(analyzed new Len bygenbach EDXS) are samples shown (analyzed as red squares. by EDXS) Lengenbach are shown chabourn as redé ite squares. Lengenbach chabournéite is located in the Pb-rich part of the diagram (the cross gives the  is locatedsquares. in Lengenbach the Pb-rich chabournéite part of the is diagram located in (the the crossPb-rich gives part theof the± diagram1 sigma (the of allcross measurements), gives the  1 sigma of all measurements), showing a higher Sb content than the samples from Jas Roux. The showing1 sigma a higherof all measurements), Sb content than showing the samples a higher from Sb Jas content Roux. Thethan nearly the samples Pb-free from dalnegroite Jas Roux. seems The to nearly Pb-free dalnegroite seems to be clearly isolated from the holotype material of this species be clearly isolated from the holotype material of this species (open squares). (open squares).

Minerals 2018, 8, 409 14 of 17

Minerals 2018, 8, x FOR PEER REVIEW 14 of 16 5. Summary and Perspective 5. Summary and Perspective Since 1958 an uninterrupted prospection for and extraction of mineral specimens has been Since 1958 an uninterrupted prospection for and extraction of mineral specimens has been performedperformed in in the the Lengenbach quar quarry.ry. Three Three working working collectives collectives have been have successively been successively in charge of in chargethese of purely these non purely-profit non-profit operations, operations, aimed at providing aimed at interesting providing specimens interesting to specimensboth science to and both sciencecollector and communities.collector communities. The Arbeitsgemeinschaft The Arbeitsgemeinschaft Lengenbach Lengenbach(AGL, literally(AGL,: Lengenbach literally: Lengenbach Working WorkingAssociation) Association) was active was from active 1958 from to 1997 1958 and to extracted 1997 and 28, extracted422 specimens 28,422 in specimenstotal. It was in followed total. It by was followedthe Interessengemeinschaft by the Interessengemeinschaft Lengenbach (IGL, Lengenbach literally(IGL,: Lengenbach literally: Interest Lengenbach Association), Interest active Association), from active1998 from to 2002. 1998 toThe 2002. IGL The produced IGL produced 2424 specimens. 2424 specimens. The Forschungsgemeinschaft The Forschungsgemeinschaft Lengenbach Lengenbach (FGL), (FGL),which which was was founded founded in 2003 in 2003 and and celebrates celebrates its its15th 15th anniversary anniversary in 2018,in 2018, has has been been extremely extremely successful.successful. The The association association could could ensure ensure thethe collaborationcollaboration of of several several experts experts as as Preferred Preferred Associated Associated Scientists,Scientists, who who performed performed countless countless investigations investigations to increase increase our our knowledge knowledge of of the the Lengenbach Lengenbach mineralogy,mineralogy, and and to to contribute contribute with with many many publicationspublications and the the description description of of several several new new mineral mineral speciesspecies to furtherto further enhance enhance Lengenbach’s Lengenbach’s reputationreputation as as an an eldorado eldorado for for rare rare and and complex complex sulfosalts. sulfosalts. In theseIn these 15 years, 15 years, 43 new 43 mineral new mineral species species have been have described been described from the from Lengenbach the Lengenbach quarry, quarry, including 17 newincluding type minerals.17 new type minerals. As a consequence of the specimen extraction performed since 2014 in the Tl-rich dolomite As a consequence of the specimen extraction performed since 2014 in the Tl-rich dolomite ribbon 1, ribbon 1, the number of thallium-bearing mineral samples extracted in the quarry has significantly the number of thallium-bearing mineral samples extracted in the quarry has significantly increased increased recently, as it was already the case in the late eighties and early nineties when the AGL recently, as it was already the case in the late eighties and early nineties when the AGL also worked in also worked in this zone (Figure 17). The FGL plans to continue the mineral prospection and thisextraction zone (Figure during 17 ).the The next FGL two plans or three to continue years in thethis mineralfascinating prospection part of the and deposit. extraction Consequently, during the nextthere two is or a threegood yearschance in to this find fascinating additional partrare thallium of the deposit. sulfosalts Consequently, and—who knows there— iseventually a good chance also to findnew additional mineral rarespecies. thallium sulfosalts and—who knows—eventually also new mineral species.

400

350

300

250

200

Number 150

100

Year FigureFigure 17. Number 17. Number of thallium of thallium bearing bearing samples samples ofﬁcially officially cataloged cataloged by the three by the working three associations, working sinceassociations, 1958. since 1958.

Author Contributions: Both authors (T.R. and P.R.) contributed to varying degrees to all the different aspects Authorof the Contributions: work that led toBoth this authorsarticle. This (T.R. includes and P.R.) conception, contributed investigations, to varying formal degrees analyses, to all the validation, different draft aspects of thepreparation, work that review led to and this editing, article. as This well includes as administration. conception, investigations, formal analyses, validation, draft preparation, review and editing, as well as administration. Funding: This research received no external funding. Funding: This research received no external funding. Acknowledgments:Acknowledgments:We We would would like like to to thank thank the the “ “VereinVerein FreundeFreunde Lengenbach”” association, association, for for its its yearly yearly financial financial contribution,contribution, and and their their members members for for their their activeactive supportsupport to the the operational operational work work in in the the quarry quarry during during their their summersumme holidays.r holidays. Special Special thanks thanks go go to to FGL’s FGL’s Scientific Scientific Head, Head, Nicolas Nicolas Meisser Meisser (Lausanne, (Lausanne, Switzerland) Switzerland) and and toto our Preferredour Preferred Associated Associated Scientists Scientists who are who always are always willing willing to investigate to investigate interesting interesting mineral mineral samples samples from from the quarry,the andquarry, without and whom without the whom incredible the incredible mineralogical mineralogical success ofsuccess the Lengenbach of the Lengenbach as worldwide-renowned as worldwide-renowned sulfosalt localitysulfosalt would locality not havewould been not possible: have been Fabrizio possible: Nestola Fabrizio (Padua, Nestola Italy), (Padua, Jakub Italy), Pl áJakubšil (Prague, Plášil (Prague, Czech Republic), Czech DanRepublic), Topa (Vienna, Dan Austria). Topa (Vienna, Thanks Austria). also go toThanks three anonymousalso go to three reviewers anonymous who substantially reviewers who helped substantially improve this work. We are also grateful to the Minerals editors for their thorough and thoughtful editing. helped improve this work. We are also grateful to the Minerals editors for their thorough and thoughtful Conflictsediting. of Interest: The authors declare no conflict of interest.

Minerals 2018, 8, 409 15 of 17

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