Lewis D. Ashwal · Bruce Cairncross

Mineralogy and origin of stichtite in chromite-bearing serpentinites

Received: 4 April 1996 / Accepted: 16 September 1996

Abstract Stichtite, a rare (14 known localities world-wide) hydrated carbonate-hydroxide of Mg and Cr withideal formula Mg6Cr2 (OH)16 CO3 · 4H2O, occurs ex-clusively in Cr-rich serpentinites of ophiolites or green-stone belts. Physical properties (hardness � 1.5–2,specific gravity � 2.16–2.2, perfect basal [0001] cleavage,grain size commonly < 100 lm) resemble talc, but themineral has an attractive purple to lilac color; chemicalanalyses demonstrate it to be a non-silicate. Stichtitegenerally occurs as irregular to rounded masses (< 1 cm– 30 cm across) and as veinlets (< 1 mm – > 2 cm wide)within serpentinite. Macroscopic and microscopic tex-tures, such as crosscutting veinlets and stringers, dem-onstrate that stichtite formation invariably post-datedserpentinization. In some specimens stichtite surroundsrelict grains of Cr-rich spinel; in others stichtite hascompletely replaced euhedral or subhedral chromites.Chemical analyses of stichtites reveal substantial sub-stitution of Al and Fe3+ for Cr in specimens from manylocalities, reflecting a possible compositional continuumbetween stichtite and rhombohedral polymorphshydrotalcite (Mg6Al2 (OH)16 CO3 · 4H2O) and pyroau-rite (Mg6Fe2 (OH)16 CO3 · 4H2O). We report the firstelectron microprobe analyses of stichtites from sevenlocalities, and summarize all available published chem-ical data. Stichtites very likely inherited part of theirtrivalent cation chemistry from precursor Cr-richspinels, but stichtite growth apparently post-datedcharacteristic ‘‘ferritchromit’’ alteration, as demon-strated by the depletion of Al and enrichment in Fe3+ instichtite relative to primary chromite core compositions.Stichtite appears to form by reaction between serpentineand altered chromite, during addition of substantialfluid, either as separate H2O and CO2 phases, or as a

mixed volatile phase. Such reactions must involve re-moval of substantial SiO2, possibly by transport andremote deposition of silica by throughgoing aqueousand carbonic fluid.

Introduction

Stichtite is a rare, attractive, lilac to purple coloredmineral familiar to many mineral collectors. It is a hy-drated carbonate-hydroxide of Mg and Cr, isostructuralwith other members of the rhombohedral PyroauriteGroup, which have the general formula Mg6R2 (OH)16CO3 · 4H2O, where R3�

� Fe, Cr, or Al. Hexagonalpolymorphs of the Sjogrenite Group include a species,barbertonite, allegedly dimorphous with stichtite(Frondel 1941):

Pyroaurite Group Sjogrenite Group1

(Rhombohedral ) (Hexagonal )

Mg6Fe2 (OH)16 CO3 · 4H2O Pyroaurite SjogreniteMg6Cr2 (OH)16 CO3 · 4H2O Stichtite Barbertonite (?)Mg6Al2 (OH)16 CO3 · 4H2O Hydrotalcite Manasseite

Although the mineral has been known for nearly acentury, no modern chemical or crystallographic workhas been carried out on stichtite since Frondel’s (1941)paper, and there is uncertainty regarding its composi-tion, crystal structure, and dimorphism. This papersummarizes available data on stichtite occurrences, andpresents new chemical data, including the first electronmicroprobe analyses to our knowledge, on specimensfrom several localities. We also discuss the petrogenesisof stichtite.

Contrib Mineral Petrol (1997) 127: 75–86 Springer-Verlag 1997

1Names of individual mineral members within each group havebeen used as group names, seemingly interchangeably in recentliterature (e.g. Palache et al. 1963; Drits et al. 1987; Roberts et al.1990). We use the original Pyroaurite and Sjogrenite Group namesas defined by Frondel (1941).

L.D. Ashwal (&) · B. CairncrossDepartment of Geology, Rand Afrikaans University,P.O. Box 524, Auckland Park, 2006, South Africa

Editorial responsibility: T. Grove

Historical aspects and occurrences

Stichtite was first defined in 1910 from material in the Adelaide Ag-Pb mine, Dundas district, Tasmania (Petterd 1910). The new min-eral was named by W.F. Petterd after an American metallurgist,Robert Sticht, general manager of Mt. Lyell Mining and RailwayCompany properties. Although the mineral had been known fromthe Dundas locality since 1891, it was incorrectly referred to until1909 as the purple variety of chlorite known as kammererite(chromian clinochlore, Nordenskiold 1840; Lapham, 1958). Thispossibility was discounted by a wet chemical analysis by A.S. Wesley(in Petterd 1910), which demonstrated the mineral to be a non-silicate. Dundas material was sent in 1912 to the Mineralogic-Petrological Institute in Zurich, and was analyzed chemically byDr. L. Hezner (1912), who suggested that the mineral represented anew chromian variety of brugnatellite (Mg6Fe3+(OH)13 CO3 · 4H2O,Artini, 1909). However, the relation of Dundas stichtite to pyroau-rite (Igelstrom 1865) and hydrotalcite (Hochstetter 1842) was re-cognized by Petterd (1910), and confirmed by Himmelbauer (1913).The results of the early research on Dundas stichtite were compiled

and translated by Twelvetrees (1914). Material from this localitywas subsequently re-analyzed by Foshag (1920).

Stichtite was next reported from chromite-bearing serpentinitesat the Megantic mine, Black Lake area, Quebec (Poitevin andGraham 1918). This region is part of the ‘‘serpentine belt’’ extendingnortheasterly from Vermont across Quebec. The first chemical an-alyses of this material, to our knowledge, are reported here.

The third, and perhaps most noteworthy occurrence of stichtite,from Kaapsehoop, in the Barberton Mountain Land of the easternTransvaal, South Africa, was described in detail by Hall (1922).Material from this locality was first recognized by E.J. Dunn in 1883,eight years before the discovery of Tasmanian stichtite (Dunn 1918),and was described as ‘‘chrometalc.... in beautiful rose-colouredplates and leaves’’ (Wilson-Moore and Wilmer 1893, p. 113). Dunnpresented a specimen of Kaapsehoop stichtite to the British Museumin 1885, but it was again mistaken for kammererite (Hall 1922).

Stichtite is now known from at least 14 localities (Table 1). Themineralogy of stichtite and related species was put into modernperspective by Frondel (1941), who furnished new crystallographicand optical data, and confirmed the polymorphism of thePyroaurite (rhombohedral) and Sjogrenite (hexagonal) Groups.

Table 1 Attributes of known stichtite localities

Locality Age ChromitePresent ?

Host Rocks AssociatedOre Deposits

References

Dundas,Tasmania

EarlyPaleozoic

Yes chromite-bearingserpentinites

Ag-Pb(Adelaide mine)

Petterd (1910)Lancaster (1977)

Kaapsehoop,Barberton Min. Land,South Africa

Archean No serpentinites asbestos(New Amianthusand other mines)

Hall (1922)

Forbes Roof,Barberton Min. Land,Swaziland

Archean No serpentinites ? Davies (1959)

Zvishavane(Shabani),Zimbabwe

Archean ? serpentinites asbestos(Shabani mine)

Laubscher (1986a)

Black Lakearea, Quebec,Canada

Silurian ? No ? asbestos(Megantic mine)

Poitevin and Graham(1918)

Marbridge, QuebecCanada

? No serpentinites Ni(Marbridge mine)

Staveley (1976)

LangmuirTownship, Ontario,Canada

? ? ? ? Mandarino (1966)

Bou-Azzer,Morocco

LateProterozoic

Yes chromite-bearingserpentinites

Co, Ni(Bou-Azzer mine)

Pallix (1978)

Cunningsburgh,Shetland islands,Scotland

? Yes chromite-bearingserpentinites

? Read and Dixon (1933)

Tereida Range(Altai Mountains),Russia

? Yes serpentinites ? Tatarinov et al. (1985)

Kazakhstan ? Yes serpentinites ? Moskaleva andIvanova (1988)

Slatinka Letovice,Czech Republic

? Yes serpentinites ? Ulrych (1966)

Campo Formoso,Bahia,Brazil

Archean ? Yes chromite-bearingserpentinites

? Boukili et al. (1963)Calas et al. (1964)

Nuggihalli,Mysore StateIndia

Archean Yes chromite-bearingserpentinites

? Varadarajan (1966)

76

Structure, physical properties and nature of occurrence

Isostructural members of the Pyroaurite Group, includ-ing stichtite, are rhombohedral, with space group R�3m.Stichtite has unit cell dimensions of a � 3:1050�4� A,c � 23:585�5�A (Ashwal et al. 1992; Kruger et al., workin preparation). The stichtite structure is similar to thatof pyroaurite, and consists of positively charged brucite-like [(Mg,Cr)(OH)2]0.25+ layers with randomly distrib-uted octahedral Mg and Cr, separated by negativelycharged interlayers �1=8 CO3 � 1=2 H2O�

0:25- containingdisordered carbonate and water.

A distinct hexagonal phase identified by X-ray ana-lyses of specimens from Kaapsehoop and Tasmania wasnamed ‘‘barbertonite’’ (Frondel 1941). The X-ray powderphotographs for ‘‘barbertonite’’ were identical to thosefor sjogrenite and manasseite, which are known hexago-nal dimorphs of pyroaurite and hydrotalcite, respective-ly. Frondel proposed, therefore, that the SjogreniteGroup consists of three hexagonal end-members (spacegroup P6/mmc, a � 3:103, A, c � 15:52, A), one ofwhich, barbertonite, is dimorphous with stichtite. De-spite extensive X-ray analysis of numerous specimensfrom the Kaapsehoop locality, including Frondel’s ho-lotype specimen, we have not been able to confirm theexistence of barbertonite, or any other hexagonal poly-morph of rhombohedral stichtite (Ashwal et al. 1992).Our crystallographic work on stichtite and specimensalleged to contain barbertonite will be published sepa-rately (Kruger et al., work in preparation).

Stichtite varies from intense lilac to rose-pink, de-pending on its mode of occurrence and extent of inter-growth with associated minerals. Hardness (1.5–2) andspecific gravity (2.16–2.2) have been determined onspecimens from Dundas, Black Lake, Cunningsburgh,and Kaapsehoop (Himmelbauer 1913; Poitevin andGraham 1918; Hall 1922; Read and Dixon 1933). Stich-tite shows perfect basal [0001] cleavage, with a greasy topearly luster. Grain size is predominantly extremelysmall. Petrographic studies showed no individual grainslarger than about 100 lm; typically stichtite specimensconsist of aggregates of platy crystals < 10–20 lm long.

Measured refractive indices of stichtites show a rangeof values: x � 1:542–1.562, e � 1:516–1.543, B � 0:016–0.028 (Himmelbauer 1913; Read and Dixon 1933;Frondel 1941; Calliere 1943, 1944; Ulrych 1966; Vara-darajan 1966; Moskaleva and Ivanova 1968). Based onhis measurements of Kaapsehoop material, Frondel(1941) assigned the higher values in the ranges he de-termined (x � 1:557, e � 1:529) to barbertonite, and forthis reason suggested that the Cunningsburgh material(x � 1:559, e � 1:543, Read and Dixon 1933) is proba-bly also barbertonite. We are skeptical about this dis-tinction, however, firstly because we could not recognizeany hexagonal phase in Barberton specimens (Ashwalet al. 1992), and secondly because mechanical separationof stichtite from (alleged) barbertonite would be nearlyimpossible, given their proposed similarity in physical

properties. A range of refractive indices (and otherphysical properties) for stichtite is likely, even for spec-imens from a single locality, given the compositionalvariation documented below.

All known stichtite occurs in association withserpentinized Cr-rich ultramafic rocks of greenstonebelts or ophiolite complexes ranging in age from Arch-ean to Paleozoic (Table 1). The original presence of Cr-rich spinel and serpentine in the host rocks appears to bea requirement for the formation of stichtite, although ina few occurrences (e.g. Kaapsehoop, South Africa) thespinel phase has been completely consumed by thestichtite-producing reactions. Other minerals associatedwith stichtite at some, but not all occurrences, are usu-ally very minor in abundance, and include carbonates(magnesite and/or dolomite), chlorite, brucite, silica(opal and/or quartz), and pyroaurite and/or sjogrenite.

In some occurrences of stichtite, the associated ser-pentine is (or was) mined for chrysotile asbestos (e.g.New Amianthus deposit, Kaapeshoop, Barberton

Fig. 1 Surface of drillcore in stichtite-bearing serpentinite fromLangmuir Township, Ontario (R.O.M. specimen M45040). Stichtite(ST) occurs as irregular masses up to 3 mm across, and clearly formedafter the fine veins and stringers of serpentine (SERP). The dark hostis composed mainly of fine grained serpentine. Long dimension ofphoto 3.5 cm

Fig. 2 Sawed surface of stichtite-bearing serpentinite from Kaapse-hoop, South Africa (specimen St-2). Network of veinlets and stringersof stichtite (ST ) in serpentinite host (SERP). Field of view 3.5 cm

77

Mountain Land, South Africa; Laubscher 1986b). Sul-fide concentrations in stichtite-bearing serpentinites havebeen mined for Ni (Marbridge deposit, Quebec; Grateroland Naldrett 1971), or Co � Ni (Bou-Azzer deposit,Morocco; Leblanc 1986). The Tasmanian stichtite isassociated with the abandoned Adelaide Pb-Ag mine(Chapman 1972).

Stichtite occurs either as irregular to rounded masses,usually less than 1 cm across (Fig. 1), or as veinletsgenerally less than 1 mm wide (Fig. 2), within a ser-pentinite host. It also coats joint surfaces or slip planes,resembling slickensides. Stichtite-bearing veins invari-ably crosscut earlier parallel fiber seams of asbestiformchrysotile, and within the veins, the orientation of finestichtite fibers is always perpendicular to the length ofthe veins. In some cases, veinlets or stringers of stichtiteform a delicate network (Fig. 2). The largest stichtitespecimens come from the Kaapsehoop, South Africalocality, where radiating to irregular masses more than30 cm across (commonly matted or contorted), andveins up to 2 cm wide (Fig. 3) are common.

In thin sections stichtite occurs as aggregates of platycrystals, generally no more than 50 lm long, distin-guishable from serpentine by slightly higher birefrin-gence and very pale pink color. In thicker sections thepink color is quite apparent. Slight pleochroism is visiblein some specimens, but the absorption formula couldnot be determined precisely. Typical stichtite texturesinclude swirling, contorted masses, surrounding relictgrains of chromite (Fig. 4). Commonly, irregular chro-mite grains are surrounded by radiating aggregates ofstichtite. Stichtite pseudomorphs after original euhedralor subhedral chromite crystals are present in somesamples (Fig. 5). Veinlets of stichtite observed under themicroscope usually show the characteristic cross-fibertexture (Fig. 6).

Analytical methods

Electron microprobe analyses were carried out on a CamecaCamebax instrument housed at Rand Afrikaans University, De-partment of Geology. Standard operating conditions for wave-length dispersive analyses were 15 kV and 15 nA. For stichtiteanalyses, beam current was reduced to 10 nA to avoid volatiliza-tion. Natural standards and conventional ZAF procedures wereused. Some specimens were analyzed with an automated energydispersive system.

Fig. 3 Hand sample showing stichtite vein crosscutting serpentinite,Kaapsehoop, South Africa (specimen St-3). The vein varies inthickness between 0.7 and 1.5 cm. The cross-fiber nature of thestichtite is apparent in the original sample. Specimen 14 cm long

Fig. 4 Photomicrograph showing relict chromite grains, partiallyaltered to ferritchromit (opaque, CH) that are surrounded by swirling,contorted masses of later stichtite. Specimen T-St-2, Dundas,Tasmania. Field of view 2.5 mm. Plane polarized light

Fig. 5a, b Photomicrograph showing relict chromite grain completelyreplaced by stichtite (ST), and surrounded by fine-grained serpentine(SERP). Specimen St-2–1, Kaapsehoop, South Africa. Field of view0.8 mm. a Plane polarized light; b Crossed polarizers

78

Bulk analyses of stichtites from Kaapsehoop, South Africa wereperformed at the Geological Survey of South Africa, Pretoria, us-ing several methods. Major elements and some minor elements(Si, Ti, Al, Fetotal, Mn, Mg, Ca, Ni) were analyzed by X-ray fluo-rescence spectroscopy (XRF), using fusion disks prepared with1.5 g of sample and 6 g of Spectoflux 105. Na was determined usingpressed powder briquettes. Matrix effects were corrected by itera-tive calculations using factors given by Norrish and Hutton (1969).Ferrous iron was determined by standard redox titration methods.Cr was determined by atomic absorption spectrophotometry usingCrO4

) leached and centrifuged from a sample fused withNa2CO3 � KClO3. Free and crystalline moisture (H2O) and H2O+)were determined by infrared absorption spectroscopy using aLECO RMC-100 instrument. C (expressed as CO2) and S weresimilarly determined using a LECO CS-244 instrument.

Chemistry

Stichtite

Chemical analysis of stichtite is problematical, mainlybecause of its fine grain size and intergrowth with otherminerals, typically serpentine or chromite. It is extremelydifficult to separate sufficient (2–3 g) pure material forclassical wet chemical analysis or routine X-ray fluo-rescence spectroscopic analysis. It is possible to over-come some of these problems using the electronmicroprobe, but in some specimens stichtite is so finelyintergrown with serpentine that even a highly focusedelectron beam (1–2 lm) cannot resolve the two minerals.Reasonable microprobe analyses of stichtite are ob-tainable by analyzing spots with minimal SiO2, prede-termined using rapid energy dispersive analysis or anaudible or visual signal for Si counts on one spectrom-eter. Stichtite also volatilizes quite readily under normalmicroprobe operating conditions, so beam current mustbe minimized.

Bulk analyses of stichtites from several localities, in-cluding wet chemical analyses published in the olderliterature, and new data by combined methods (de-scribed above) for samples from Kaapsehoop, SouthAfrica are given in Table 2. These results are of variable

quality. Most of the samples obviously contained im-purities, mainly serpentine, as demonstrated by thepresence of substantial SiO2. Material analyzed fromCunningsburgh, Scotland (col. 7) was reported to con-tain admixed serpentine and chromite (Read and Dixon1933), accounting for the excess Si and Cr in the analysisand the formula computed therefrom. We also suspectthat the Brazilian stichtite (col. 9) contains admixtures ofother phases (mainly chromite?) because of the highMgO and Cr2O3 values. The bulk analyses of stichtitefrom Dundas, Tasmania (col. 4) and Nuggihalli, India(col. 6) do not include Al2O3, and are, therefore, in-complete, as can be seen by the low summation for theIndian material. Analyses of H2O+, H2O) and CO2 instichtite are problematical because of their large abun-dances and the low volatilization temperatures. In onecase (stichtite from Kazakhstan, col. 8), volatiles arereported only as loss on ignition; we computed an idealH2O/CO2 ratio for formula calculation of this sample.

The problem of impurities can be partially resolvedby using the electron microprobe. For this purpose, weobtained stichtite specimens from as many localities aspossible; representative microprobe analyses of thesesamples are given in Table 3. The data shown representselected individual spot analyses for which SiO2 wasminimal, indicating little or no admixture of fine grainedserpentine under the microprobe beam. Chromite iseasily avoided by this technique. Mineral formulae cal-culated from the microprobe data are much closer toideal stichtite stoichiometry (cf. Tables 2, 3). There is,however, a slight but consistent excess of divalent cat-ions (mainly Mg) and deficiency of trivalent cations inthe microprobe data, suggesting possible multivalency ofMn, Ni, and/or minor substitution Mg into the R3+ site.Total cation values are as close to ideal as can be ex-pected, given the analytical difficulties.

Based upon the available and newly acquired chem-ical data, it is apparent that natural stichtites are vari-able in composition, with substantial substitution ofFe3+ and Al for Cr in the trivalent cation site. Compo-sitions can be conveniently portrayed on a triangulardiagram (Fig. 7), with apices corresponding to pure end-members: pyroaurite (Fe3+), hydrotalcite (Al), andstichtite (Cr). The purest stichtites (with > 98 mol% Crend-member) are those from the Black Lake area,Quebec; specimens from all other localities contain > 15mol% pyroaurite and hydrotalcite components (Fig. 7).Stichtites from Kaapsehoop, South Africa show rela-tively constant and low Al (4–8 mol% hydrotalcitecomponent) but intermediate and variable Cr/Fe3+.Samples from Morocco, Ontario, and India extend tohigher Cr/Fe3+, with progressively decreasing Al(Fig. 7). Substantial Al is found in material from theAltai Mountains, Russia (18–34 mol% hydrotalcite),Zvishavane, Zimbabwe (22–27 mol% hydrotalcite),Kazakhstan (26 mol% hydrotalcite), and Tasmania(10–31 mol% hydrotalcite). Some of the variability ofindividual sample fields may be due to admixture underthe microprobe beam of extremely fine grained sheet

Fig. 6 Photomicrograph showing vein of stichtite (ST ) crosscuttingearlier-formed serpentinite (SERP). The cross-fiber structure of thestichtite is visible. Specimen St-2-2, Kaapsehoop, South Africa. Fieldof view 2.8 mm. Plane polarized light

79

silicates (serpentine or chlorite), as discussed below(under the heading of Serpentine).

Based upon our new bulk analyses of material fromKaapsehoop, South Africa (Table 2), we conclude thatstichtite contains very little, if any Fe2+, most of thereported FeO in these and other bulk analyses probablycomes from admixed chromite and/or serpentine. Otherchemical features of note are the high contents of H2O,CO2, and Ni; the latter is confirmed by microprobe

analysis for samples from Kaapsehoop, Tasmania,Morocco, and Ontario (Table 3).

Chromite

Relict Cr-rich spinel occurs in association with moststichtites (Table 1), a notable exception being Kaapse-hoop, South Africa, where only pseudomorphs of

Table 2 Bulk analyses of stichtites

1a 2 3 4 5 6 7 8 9

Kaapsehoop, South Africa Dundas, Tasmania Nuggihalli,India

ShetlandIsl.,Scotland

Kazakhstan Bahia,Brazil

IdealStichtite

SiO2 2.91 0.63 4.50 3.87 2.09 8.51TiO2 <0.1 <0.1Al2O3 0.24 1.04 0.90 2.24 1.10 3.8 1.80Cr2O3 8.59 9.26 8.90 20.44 14.08 12.89 27.10 15.1 23.48 23.24Fe2O3 5.93 5.62 10.60 4.04 2.59 8.52 1.5 1.51FeO 0.10 0.11 0.85 1.10 0.28 8.95MnO 0.20 0.05 0.05NiO 0.15 0.07 0.10 0.40MgO 35.37 39.56 36.70 37.12 36.59 37.65 26.72 37.0 40.00 36.98CaO <0.1 <0.1 tr 0.10Na2O 0.05H2O) 6.52 3.09 3.65 0.95 0.24 1.59H2O+ 34.20 34.45 26.80 26.31 33.01 26.56 17.46 17.46c 21.70 33. 05b

CO2 6.29 6.92 6.90 10.45 6.94 10.92 3.14 3.14c 9.58 6.72S 0.03 <0.00

100.53 100.80 99.95 100.24 99.27 90.60 99.89 100.0 100.06 100.00

Formulae per 23 oxygens

Si 0.292 0.065 0.495 0.429 0.235 ) 1.128 ) ) )Ti <0.008 <0.008 ) ) ) ) ) ) ) )

Al 0.028 0.126 0.117 ) 0.285 ) 0.172 0.478 0.248 )Cr 0.681 0.752 0.774 1.790 1.201 1.216 2.840 1.259 2.173 2.000Fe3+ 0.447 0.434 0.878 ) 0.338 0.233 0.650 0.126 0.133 )

1.156 1.312 1.769 1.790 1.824 1.449 3.662 1.883 2.554 2.000

Fe2+ 0.008 0.009 0.078 0.102 0.025 ) 0.992 ) ) )Mn 0.017 0.004 ) ) ) ) 0.006 ) ) )Ni 0.012 0.006 0.009 ) ) ) ) ) 0.038 )Mg 5.285 6.057 6.021 6.128 5.884 6.699 5.279 5.797 6.990 6.000Ca <0.011 <0.011 ) ) ) ) 0.014 ) )

5.333 6.067 6.108 6.230 5.909 6.699 6.291 5.797 7.028 6.000

Hb 27.225 25.718 22.351 20.137 23.751 21.137 15.645 24.707** 18.182 24.000C 0.861 0.970 1.037 1.580 1.022 1.779 0.568 1.027** 1.531 1.000

Totalcations

34.874 34.160 31.759 30.165 32.721 31.065 27.297 33.394 29.283 33.000

a1. Stichtite, Kaapsehoop, Barberton Mountain Land, South Africa, collected May 1991 by Ashwal and Cairncross, new data, this paper2. Stichtite specimen labeled ‘‘barbertonite’’ in R.A.U. collection, new data, this paper3. Stichtite, Kaapsehoop, Barberton Mountain Land, South Africa, analysis reported in Hall (1992)4. Stichtite, Dundas, Tasmania (Hezner, in Twelvetrees 1914). Note Al2O3 not determined5. Stichtite, Dundas, Tasmania (Foshag 1920)6. Stichtite, Nuggihalli Schist Belt, Mysore State, India (Varadarajan 1996), Note Al2O3 not determined7. Impure stichtite, Cunningsburgh, Shetland islands, Scotland (Read and Dixon 1933), contains admixed chromite and serpentine8. Stichtite, Kazakhstan (Moskalava and Ivanova 1968)9. Stichtite, Campo Formoso, Bahia, Brazil (Calas et al 1984)bTotal H2O as H2O+

cReported as H2O + CO2; computed as ideal H2O/CO2 ratio

80

stichtite after chromite are present (Fig. 5). Among thesamples we obtained, chromite is present in materialfrom Dundas, Tasmania; Bou-Azzer, Morocco; andCunningsburgh, Scotland. Representative microprobeanalyses are given in Table 4, and compositions areplotted in Fig. 8.

Table 3 Representative microprobe analyses of stichtites

1a 2 3 4 5 6 7 IdealStichtite

SiO2 0.00 0.38 0.00 0.01 0.00 0.00 0.00TiO2 0.00 0.11 0.00 0.07 0.05 0.00 0.01Al2O3 0.72 3.36 0.54 0.31 0.09 1.25 4.75Cr2O3 14.14 11.78 22.66 19.41 26.24 15.57 9.00 23.24Fe2O3

b 11.24 2.94 9.19 5.15 0.09 3.91 12.98NiO 0.18 0.14 0.23 0.07 0.01 0.00 0.00MnO 0.06 0.40 0.00 0.10 0.07 0.00 0.04MgO 45.39 37.04 58.43 44.23 47.87 36.24 45.33 36.98CaO 0.00 0.14 0.00 0.01 0.03 0.00 0.01Na2O 0.02 0.00 0.00 0.02 0.00 0.00 0.00K2O 0.02 0.00 0.01 0.00 0.02 0.00 0.00

71.77 56.29 91.06 69.38 74.47 56.97 72.12 60.22

Formulae per 9 oxygens

Si 0.000 0.043 0.000 0.001 0.000 0.000 0.000Ti 0.000 0.009 0.000 0.004 0.003 0.000 0.000

Al 0.077 0.446 0.046 0.034 0.009 0.168 0.497Cr 1.020 1.050 1.285 1.445 1.814 1.400 0.632 2.000Fe3+ 0.772 0.249 0.496 0.385 0.006 0.335 0.867

1.869 1.745 1.827 1.844 1.829 1.903 1.996 2.000

Mn 0.005 0.038 0.000 0.008 0.005 0.000 0.003Mg 6.175 6.124 6.247 6.207 6.240 6.146 5.999 6.000Ni 0.013 0.009 0.013 0.005 0.001 0.000 0.000

6.193 6.171 6.260 6.220 6.246 6.146 6.002 6.000

Ca 0.000 0.017 0.000 0.001 0.003 0.000 0.001Na 0.004 0.000 0.000 0.004 0.000 0.000 0.000K 0.002 0.000 0.001 0.000 0.002 0.000 0.000

Total Cations 8.068 8.075 8.088 8.074 8.083 8.049 7.998 8.000

a1. Stichtite, Kaapsehoop, Barberton Mountain Land, South Africa, specimen ST-32. Stichtite, Stichtite Hill, Dundas, Tasmania, Museum of Victoria specimen M178023. Stichtite, Bou-Azzer, Morocco, Royal Ontario Museum (R.O.M.) specimen M316844. Stichtite, Langmuir Township Cochrane District, Ontario, R.O.M. specimen M450405. Stichtite, Megantic Mine, Black Lake area, Quebec, Harvard Museum specimen 951956. Stichtite, Hoo Field, Cunningsburgh, South Mainland, Shetland Islands, Scotland, British Museum specimen BM 1936, 12927. Stichtite, Zvishavani (Shabani), Zimbabwe, specimen SHE-2

b Total Fe as Fe2O3

Fig. 7 Compilation of available stichtite compositions from 11localities, plotted in terms of trivalent cation end-members. Formicroprobe data collected in this study (dots), all Fe is assumed to beFe3+. Bulk analyses (by wet chemical, XRF, and other methods) areshown as squares (data sources given in Table 1). Localities: BRA(Bahia, Brazil), IND (Nuggihalli, India), KAZ (Kazakhstan), MOR(Bou-Azzer, Morocco), ONT (Langmuir Township, Ontario), QUE(Black Lake, Ontario), RSA (Kaapsehoop, South Africa), SCO(Cunningsburgh, Scotland), TAS (Dundas, Tasmania), ZIM (Shabani,Zimbabwe). Al2O3 was not reported in the analysis of material fromIndia

b

81

Partial alteration of Cr-rich spinel is common inserpentinites (e.g. Burkhard 1993), but areas preservingpresumed original compositions can generally be dis-tinguished on textural grounds. In our stichtite-bearingspecimens, cores of chromite grains are compositionallyhomogeneous, with low Fe3+ (0–4 wt% Fe2O3) and in-termediate Mg/Mg+Fe2+ (0.41–0.67). Cr/Cr+Al ratiosare high, with each specimen having a distinct range(Tasmania: 0.56–0.59; Scotland: 0.68–0.78; Morocco:0.83–0.85). These may represent primary compositions,and overlap with the fields for chromites from Alpine-type peridotites in terms of Mg/Fe2+ and Cr/Al (Dickand Bullen 1984).

Alteration of these chromites produces Al- and Mg-poor, Fe-rich spinels with variable Fe3+/Cr, which occureither as rims (Scotland) or as irregular veins (Tasma-nia). These spinels are enriched in NiO (up to 2.3 wt%),and to a lesser degree MnO (Table 4). Such composi-tions are frequently reported from chromite-bearingserpentinites (Haggerty 1976), and have been referred toas ‘‘ferritchromit’’ (Spangenberg 1943). The origin of‘‘ferritchromit’’ has been discussed in terms of severalprocesses (Wylie et al. 1987), including overgrowths onchromite cores during serpentinization (Ulmer 1974)and prograde metamorphic reaction between chromitecores and magnetite rims formed during serpentinization(Bliss and MacLean 1975). Interestingly, the ‘‘ferritchr-

omit’’ analyses from Cunningsburgh (Scotland) plotalong a continuum of compositions between chromitecores and magnetite, which occurs both intergrown withserpentine and as crosscutting veins (Fig. 8). This tra-jectory resembles the miscibility gap for Cr-Al-Fe3+

spinels proposed by Loferski and Lipin (1983).In terms of the trivalent cations (Al, Cr and Fe3+),

stichtites are invariably depleted in Al, and enriched inFe3+ relative to presumed primary chromite composi-tions (Fig. 8). In the case of Cunningsburgh (Scotland)material, stichtite compositions plot on the spinel alter-ation trajectory described above (Fig. 8). Compositionalrelations between stichtite and other phases are dis-cussed below, under Petrogenesis.

Serpentine

Serpentine is ubiquitously associated with stichtite. Inthe older literature, all three polymorphs of serpentinehave been reported to coexist with stichtite, but detailedX-ray study of serpentine mineralogy is beyond thescope of our paper. Nevertheless, representative ser-pentine microprobe analyses from six stichtite specimensare given in Table 5. Most serpentine compositions areunremarkable, but in sample 17802 from Dundas Tas-mania, we analyzed by energy dispersive microprobe

Table 4 Representative microprobe analyses of spinels associated with stichtites

1a 2 3 4 5

SiO2 0.00 0.00 0.00 0.00 0.00TiO2 0.04 0.01 0.17 0.06 0.15Al2O3 22.40 0.04 11.26 0.62 8.49Cr2O3 45.30 23.45 57.60 31.49 63.32Fe2O3

b 4.06 47.59 4.36 39.74 0.00FeOb 14.14 20.19 12.81 21.80 18.56NiO 0.11 2.34 0.12 0.95 0.00MnO 0.23 1.35 0.85 0.96 0.31MgO 13.79 4.90 13.26 5.40 9.60CaO 0.03 0.00 0.00 0.00 0.00

100.07 99.87 100.43 101.02 100.43

Formulae per 4 oxygens and 3 cationsa

Si ) ) ) ) )Ti 0.001 ) 0.004 0.002 0.004Al 0.808 0.002 0.426 0.026 0.332Cr 1.096 0.681 1.461 0.895 1.664Fe3+ 0.094 1.317 0.105 1.075Fe2+ 0.362 0.621 0.344 0.656 0.516Mn 0.006 0.042 0.023 0.029 0.009Mg 0.629 0.268 0.634 0.289 0.475Ni 0.003 0.069 0.003 0.027 )Ca 0.001 ) ) ) )

3.000 3.000 3.000 3.000 3.000

a1. Tasmania M17802, chromite core2. Tasmania M17802, ferritchromit rim3. Scotland BM 1936, chromite4. Scotland BM 1936, ferritchromit5. Morocco M31685, chromite

bCalculated assuming ideal stoichiometry

82

methods 160 spots in a 1 mm2 grid within an area offinely intergrown stichtite and serpentine. The results,plotted in Fig. 9, show that in addition to typical ser-pentine, with < 1.5 wt% Al2O3, there is an additionalphase, with up to 7 wt% Al2O3, that we regard as Al-richserpentine. The scattering of points intermediate be-tween stichtite (SiO2 < 1 wt%) and this Al-rich serpen-tine phase probably represents mixtures of the twominerals unresolvable by the microprobe beam. SimilarAl-rich serpentines, with Al2O3 up to 5.8 wt% were de-scribed by Frost (1975).

Petrogenesis

Several balanced stichtite-producing reactions can bewritten, none of which has been investigated experi-mentally, and none of which is individually satisfactoryto explain all of the features of stichtite occurrences:

2 serpentine � chromite � 8 H2O � CO2

� stichtite � 4 quartz � FeO �1�

3 serpentine � chromite � 7 H2O � CO2

� stichtite � talc � 4 quartz � FeO �2�

6 magnesite � chromite � 12 H2O

� stichtite � 5 CO2 � FeO �3�

6 brucite � chromite � 6 H2O � CO2

� stichtite � FeO �4�

The involvement of both serpentine (as a source ofMg) and chromite (as a source of Cr, Al, and Fe) asprecursor phases necessary for the production of stich-tite seems certain, given the ubiquitous presence of ser-pentine in all occurrences of stichtite, and the presenceof relict chromite and/or pseudomorphs of stichtite afterchromite in most occurrences. Reactions (1) and (2),involving the breakdown of serpentine � chromite toform stichtite are perhaps most appealing, given thetextural relations, but some mechanism must be calledupon for removal of substantial SiO2 released fromserpentine, because no quartz, talc, or other SiO2-richphases are present in direct association with stichtite-bearing rocks. One possibility involves transport andremote redeposition of dissolved silica by throughgoingaqueous and/or carbonic fluid. Likewise, the FeO re-leased from chromite breakdown is not accommodatedin stichtite; it may be partially oxidized and taken up asmagnetite, and/or removed in solution.

Fig. 8 Triangular diagrams showing microprobe compositions ofspinels (chromite, ferritchromit, magnetite, filled circles) and coexis-ting stichtite (open circles) from 3 localities. Fe3+ content of spinel wascalculated assuming ideal stoichiometry. For stichtite, all Fe isassumed to be Fe3+

b

83

Reactions (3) and (4) obviate the need for silica re-moval during stichtite formation; this obviously wouldhave taken place during production of magnesite orbrucite from original ultramafic rocks. Small amounts ofmagnesite have been reported in some ultramafic rocksassociated with stichtite, for example at Black LakeQuebec, Langmuir, Ontario, Dundas, Tasmania, andCampo Formoso, Brazil (references, Table 1). Neithermagnesite nor brucite was found in any of the specimenswe analyzed.

The reactions above ignore the fact that naturalstichtites and chromites are chemically more complex

Table 5 Representative microprobe analyses of serpentines associated with stichtites (na not analyzed)

1a 2a 3a 4a 5a 6a

SiO2 39.34 38.54 41.58 42.98 39.54 41.99TiO2 0.10 0.00 0.00 0.00 0.03 0.08Al2O3 0.53 1.40 0.00 0.26 0.17 0.16Cr2O3 0.82 1.42 0.00 0.00 0.79 0.52FeOb 2.85 2.97 1.21 0.93 2.79 1.31NiO 0.18 0.00 na na 0.24 0.21MnO 0.01 0.00 0.00 0.00 0.03 0.14MgO 37.64 37.24 38.50 38.69 43.42 43.34CaO 0.00 0.00 0.15 0.00 0.00 0.04Na2O 0.01 na na na 0.00 0.00K2O 0.01 na na na 0.00 0.03

81.49 81.57 81.44 82.86 87.01 87.79

Formulae per 7 oxygens

Si 1.875 1.938 2.054 2.077 1.875 1.946Ti 0.004 – – – 0.001 0.003

Al 0.031 0.083 – 0.015 0.009 0.009Cr 0.033 0.056 – – 0.030 0.019Fe2+ 0.120 0.125 0.050 0.038 0.111 0.051Mn 0.000 – – – 0.001 0.005Mg 2.818 2.791 2.835 2.787 3.069 2.994Ni 0.007 0.009 0.008

3.009 3.055 2.885 2.840 3.229 3.086

Ca – – 0.008 – – 0.002Na 0.001 – – – – –K 0.001 – – – – 0.002

Total cations 4.990 4.993 4.946 4.917 5.105 5.039

a 1. Kaapsehoop St-2-12. Tasmania 178023. Quebec 951954. Scotland BM 19365. Ontario M450406. Morocco M31685

b Total Fe as FeO

Fig. 9 Energy dispersive microprobe analyses �n � 160� of finelyintergrown stichtite and serpentine from sample 17802 (Dundas,Tasmania), carried out within a grid of 1 mm2. Stichtite (SiO2 < 1wt%) is apparently intergrown with an Al-rich serpentine (Al2O3 3–7wt%) in addition to typical Al-poor serpentine (Al2O3 < 1.5 wt%).Points intermediate between stichtite and Al-rich serpentine probablyrepresent fine intergrowths of the two phases, unresolvable by themicroprobe beam

b

84

then their end-member compositions. However, stich-tites do not simply inherit the trivalent cation chemistryof precursor chromites, as is shown by the Al-Cr- Fe3+

relations in samples containing both phases (Fig. 8).Stichtite compositions are enriched in Fe3+ and depletedin Al relative to presumed primary chromites, and liepart way toward chromite alteration products, such as‘‘ferritchromit’’ and magnetite that formed during ser-pentinization. In one case, stichtite compositions plot ona chromite alteration trajectory (Fig. 8). These stichtites,therefore, appear to be the products of reactions in-volving altered chromites; this is consistent with texturalevidence that stichtite formation post-dates serpent-inization.

A prerequisite for stichtite formation is the additionof substantial fluid, either as separate H2O and CO2phases, or more likely, as a mixed volatile phase. Ser-pentine minerals are highly unstable in the presence ofCO2-rich fluid, and commonly react to form talc-car-bonate and/or quartz-carbonate assemblages (Cherno-sky et al. 1988). The absence or paucity of talc, quartz,and carbonates in association with stichtites suggeststhat a unique set of conditions must prevail for stichtiteformation from serpentine-bearing precursors. It is dif-ficult to specify or even speculate on these conditions inthe absence of thermodynamic and stability data forstichtite. The common occurrence of stichtite as veinscrosscutting serpentine could be taken as evidence forinflux of a CO2-bearing fluid during a separate eventthat post-dates serpentinization. However, late carbon-atization may have followed serpentinization as fluidcomposition evolved during a single infiltration event. Insuch cases conclusions based on textural evidence can bemisleading (O’Hanley 1997).

Discussion and suggestions for future work

Given the fact that CO2 influx into serpentinites is quitecommon, and has been documented, for example, inmany greenstone belts (e.g. Veizer et al. 1989), the rarityof stichtite is somewhat puzzling. It is likely that smallamounts of stichtite have been overlooked in somechromite-bearing serpentinites. Bliss and MacLean(1975, p. 978), for example, report the presence of apyroaurite-group mineral, perhaps a ‘‘mixture ofpyroaurite and stichtite’’, that replaces ferritchromitrims on chromites from serpentinites of the ThompsonNickel Belt, Manitoba. However, unusual conditions oftemperature, pressure, fluid composition, and fO2 ,combined with efficient pathways for silica removal, maybe required to produce stichtite rather than more com-mon assemblages containing talc, quartz and magnesite.Thermochemical data, and experimental studies onstichtite stability will be required to interpret theseconditions.

The existence of barbertonite as a hexagonal dimorphof stichtite should be re-investigated, inasmuch as ourstudies failed to confirm this phase even in holotype

specimens. TEM studies may be needed for this becausethe fine grain size typical of natural occurrences en-cumbers the distinction of stichtite and barbertonite byroutine X-ray methods.

Acknowledgements We thank C.A. Francis (Harvard Mineralogi-cal Museum, Cambridge, MA), J.A. Mandarino (Royal OntarioMuseum, Toronto), P.J. Dunn (Smithsonian Institution, Wash-ington D.C.), and A.M. Clark (British Museum, London) forproviding stichtite samples from their collections. J. Totterdell(Australian Geological Survey Organization, Canberra), J.A. Per-cival (Geological Survey of Canada, Ottawa), M. Sukhanov(Russian Academy of Sciences, Moscow), and R. Dixon (Councilfor Geoscience, Pretoria) supplied copies of articles that were dif-ficult for us to obtain. M. Cloete (Council for Geoscience, Pretoria)kindly arranged for new bulk analyses of Kaapsehoop stichtites.Some microprobe analyses were performed by R.A.U. students andstaff: M. Beattie, B. Saunders, C. Day, S. Theron, L. Stephan, J.Gutzmer, and V. Morel. This research was supported by theFoundation for Research and Development (RSA).

References

Ashwal LD, Cairncross B, Kruger G, van Schalkwyk J (1992)Stichtite: occurrence, chemistry, crystallography and petrogen-esis (abstract). 24th Geocongress, Geol Soc S Afr, Bloemfon-tein, pp 17–19

Artini E (1909) Brugnatellite: nuova specie minerale trovata in ValMalenco. Rendiconti Della Reale Accademia dei Lincei, Roma18 [5]: 3–6

Bliss NW, MacLean WH (1975) The paragenesis of zoned chromitefrom central Manitoba. Geochim Cosmochim Acta 39: 973–990

Boukili H, Novikoff A, Besnus Y, Soubies F, Queiroz C (1983)Petrologie des produits de l’alteration des roches ultrabasiquesa chromites de Campo Formoso, etat de Bahia, Brasil. SciencesGeologiques 72: 19–28

Burkhard DJM (1993) Accessory chromium spinels: their coexis-tence and alteration in serpentinites. Geochim Cosmochim Acta57: 1297–1306

Calas G, Manceau A, Novikoff A, Boukili H (1984) Comportementdu chrome dans les mineraux d’alteration du gisement deCampo Formoso (Bahia, Brasil). Bull Mineral 107: 755–766

Calliere S (1943) Sur les caracteres specifiques d’un group d’hy-drocarbonates magnesiens. Bull Soc Fr Mineral 66: 494–502

Calliere S (1944) Sur les caracteres specifiques de l’hydrotalcite. CR Acad Sci Paris 219: 256–258

Chapman AH (1972) On a spectacular find of crocoite in theAdelaide mine, Dundas, Tasmania. Mineral Rec 3: 111–113

Chernosky JV Jr, Berman RG, Bryndzia LT (1988) Serpentine andchlorite equilibria. In: Bailey SW (ed) Hydrous phyllosilicates,(Reviews in Mineralogy vol. 19). Mineralogical Society ofAmerica, Washington DC, pp 295–346

Davies DN (1959) The intrusion of the Jamestown igneous com-plex in Swaziland (with discussion). 20th Int Geol Congr,Mexico City, 1956, Assoc de Serv Geol Afr, Actas y Trabajos,pp 69–74

Dick HJB, Bullen T (1984) Chromian spinel as a petrogenetic in-dicator in abyssal and alpine-type peridotites and spatially as-sociated lavas. Contrib Mineral Petrol 86: 54–76

Drits VA, Sokolova TN, Sokolova GV, Cherkashin VI (1987) Newmembers of the hydrotalcite-manasseite group. Clays and ClayMinerals 35: 401–407

Dunn EJ (1918) Early history of the South African diamond fields.Industrial Australian and Mining Standard 60:775, Melbourne,July 18, 1918 [Mineral Abstr 1: 47]

Foshag WF (1920) The chemical composition of hydrotalcite andthe hydrotalcite minerals. Proc US Nat Mus 58: 147–153[Mineral Abstr 1: 175]

85

Frondel C (1941) Constitution and polymorphism of the pyroauriteand sjogrenite groups. Am Mineral 26: 295–315

Frost BR (1975) Contact metamorphism of serpentinite, chloriticblackwall and rodingite at Paddy-go-Easy Pass, Central Cas-cades, Washington. J Petrol 16: 272–313

Graterol M, Naldrett AJ (1971) Mineralogy of the Marbridge No. 3& No. 4 nickel-iron sulfide deposit. Econ Geol 66: 886–900

Haggerty SE (1976) Opaque mineral oxides in terrestrial igneousrocks. In: Rumble D III (ed) Oxide minerals (Mineral Soc AmShort-Course Notes 3)-Mineralogical Society of America,Washington DC, pp HG1–HG100

Hall AL (1922) On a new occurrence of stichtite from the Bar-berton district. Trans Geol Soc S Afr 24: 182–187

Hezner L (1912) On a new chrome-bearing magnesium hydroxy-carbonate. Centralblatt Mineral 18: 569

Himmelbauer A (1913) Zur Kenntniss des Minerals Stichtit.Tschermaks Mineral Petrogr Mitt 32: 135–137

Hochstetter C (1842) Untersuchung uber die Zusammensetzungeiniger Mineralien. Journal Prakt Chem 27: 376

Igelstrom LJ (1865) New and rare minerals from Vermlands andOrebo Provinces (in Swedish). Ofversigt af Kongl. Vetenskaps-Akademiens Forhandlingar, Stockholm 9: 605–613

Lancaster K (1977) That elusive stichtite. Australian Mineral 1: 28–29

Lapham DM (1958) Structural and chemical variation in chromi-um chlorite. Am Mineral 43: 921–956

Laubscher DH (1986a) Chrysotile asbestos in the Zvishavane(Shabani) and Mashava (Mashaba) areas, Zimbabwe. In: An-haeusser CR, Maske S (eds) Mineral deposits of southern Af-rica. Geol Soc S Afr, Johannesburg, pp 377–393

Laubscher DH (1986b) The New Amianthus chrysotile asbestosdeposit, Kaapsehoop, Barberton greenstone belt. In: An-haeusser CR, Maske S (eds) Mineral deposits of southern Af-rica. Geol Soc S Afr, Johannesburg, pp 421–426

Leblanc M (1986) Co-Ni arsenide deposits with accessory gold,in ultramafic rocks from Morocco. Can J Earth Sci 23:1592–1602

Loferski PJ, Lipin BR (1983) Exsolution in metamorphosed chro-mite from the Red Lodge district, Montana. Am Mineral 68:777–789

Mandarino JA (1966) Pyroaurite and stichtite from Langmuirtownship, Ontario (abstract). Can Mineral 8: 668–669

Moskaleva VN, Ivanova VP (1968) The hydrotalcite mineral groupin serpentinites (in Russian). Zap Vseso Mineral Ova 97(2):172–184

Nordenskiold N (1840) Description of kammererite, a new mineralfrom Siberia (in Swedish). Acta Soc Sci Fenn 1, 1: 483–487

Norrish K, Hutton JT (1969) An accurate X-ray spectrographicmethod for the analysis of a wide range of geological samples.Geochim Cosmochim Acta 33: 431–453

O’Hanley DS (1997) Serpentinites and rodingites as records ofmetasomatism and fluid history. In: de Wit MJ, Ashwal LD(eds) Greenstone belts, Oxford Univ Press Monographs onGeol and Geophys No 35, pp. 164–175

Palache C, Berman H, Frondel C (1963) The system of mineralogy.7th Ed, John Wiley & Sons, NY, 834 pp

Pallix G (1978) Famous mineral localities: Bou-Azzer, Morocco.Mineral Rec 9: 69–73

Petterd WF (1910) Catalogue of the minerals of Tasmania. MinesDept Publ, John Vail Printers, Government Printer, Hobart,pp. 167–169

Poitevin E, Graham RPD (1918) Contributions to the mineralogyof Black Lake area, Quebec. Can Geol Surv Mus Bull 27

Read H, Dixon BE (1933) On stichtite from Cunningsburgh,Shetland Islands. Mineral Mag 23: 309–316

Roberts WL, Campbell TJ, Rapp GR Jr (1990) Encyclopedia ofminerals. 2nd Ed, Van Nostrand Reinhold Co, NY, 979 pp

Spangenberg K (1943) Die Chromitlagerstatte von Tampadel amZobten. Zeit Prakt Geol 51: 13–55

Staveley RC (1976) Minerals of Marbridge Mines, Ltd. MineralRec 7: 174–178

Tatarinov AV, Sapozhnikov AN, Prokudin S, Frolova LP (1985)Stichtite in serpentinites of the Terekta Ridge (Gornyi Altai) (inRussian). Zap Vseso Mineral Ova 114(5): 575–581

Twelvetrees WH (1914) Stichtite. A new Tasmanian mineral. Notesby various authors, collected and edited. Tasmania Dep Mines,Geol Surv Rec No 2

Ulmer GC (1974) Alteration of chromite during serpentinization inthe Pennsylvania-Maryland District. Am Mineral 59: 1236–1241

Ulrych J (1966) Stichtite from serpentine deposits of Slatinka,Letovice. Cas Mineral Geol 3, 11:311–315 (in Czech, Englishsummary in Chem Abstr 68: 14727 h)

Varadarajan S (1966) Stichtite from the ultramafics of Nuggihallischist belt, Mysore state (abstract). Proc Indian Sci Congr, 53rdSessn, Chandigarh, Part 3, p 183

Veizer J, Hoefs J, Ridler RH, Jenses LS, Lowe DR (1989) Geo-chemistry of Precambrian carbonates: I. Archean hydrothermalsystems. Geochim Cosmochim Acta 53: 845–857

Wilson-Moore C, Wilmer WHC (1893) The minerals of southernAfrica. Argus Press, Johannesburg

Wylie AG, Candela PA, Burke TM (1987) Compositional zoning inunusual Zn-rich chromite from the Sykesville district ofMaryland and its bearing on the origin of ‘‘ferritchromit’’. AmMineral 72: 413–422

86