Clay Minerals, (2013) 48, 143–148

Stichtite: a review

F. L. THEISS, G. A. AYOKO AND R. L. FROST*

School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, Brisbane Queensland 4001, Australia

(Received 28 August 2012; revised 11 October 2012; Editor: John Adams)

ABSTRACT: Stichtite is a naturally occurring layered double hydroxide (LDH) with the ideal chemical formula Mg6Cr2CO3(OH)16·4H2O. It has received less attention in the literature than other LDHs and is often described as a rare mineral; however, abundant deposits of the mineral do exist. In this article we aim to review a number of significant publications concerning the mineral stichtite, including papers covering the discovery, geological origin, synthesis and characterizsation of stichtite. Characterization techniques reviewed include powder X-ray diffraction (XRD), infrared spectroscopy (IR), near infrared spectroscopy (NIR), Raman spectroscopy (Raman), thermo- gravimetry (TG) and electron microprobe analysis.

KEYWORDS: stichtite, layered double hydroxide, anionic clays, hydrotalcite, synthesis, X-ray powder diffraction, thermal analysis, IR spectroscopy, near-IR spectroscopy, Raman spectroscopy, electron microprobe analysis.

The mineral stichtite is a -substituted (Mg6Al2CO3(OH)16·4H2O), the most commonly layered double hydroxide (LDH) which occurs in studied LDH, Al3+ is substituted with Cr3+in the nature. Unlike many other LDHs, little has been same way as Fe3+ substitutes for Al3+ in pyroaurite published on stichtite. One of the reasons for this (Mg6Fe2CO3(OH)16·4H2O). Samples of naturally oversight may be the perceived rarity of stichtite, occurring stichtite often exhibit varying degrees of which is known to exist only in a limited number of partial substitution of Cr3+ in the cation layers for locations around the world. One of these locations Al3+ or Fe3+ (Ashwal & Cairncross, 1997). is Tasmania, Australia, where the mineral was first Stichtite is an interesting and potentially under- discovered and where significant deposits may still utilized resource as evident by the limited number be found. Layered double hydroxides (which are of publications available in the literature. Currently also known as anionic clays or hydrotalcites) are a stichtite is primarily valued only for its intense group of layered clay minerals that are described by purple to pink colour (which depends on impurities the general formula: present) resulting in its popularity as a semi- precious stone and as a curiosity in mineral [M2+ M3+(OH) ]x+[AnÀ] ·mH O (1) 1–x x 2 x/n 2 collections. The only practical application of where M2+ and M3+ are the divalent and trivalent stichtite is as a minor source of metallic chromium. layer cations respectively, 0.2 < x < 0.33 and AnÀ is This paper aims to provide a comprehensive review the exchangeable anion which is often (but not of the published literature on the mineral and make always) carbonate (Labajos & Rives, 1996; Rives, recommendations for possible future work. 2001, 2002; Frost et al., 2007, 2009). The ideal chemical formula of stichtite is Mg Cr CO (OH) 6 2 3 16 DISCOVERY AND EARLY ·4H O. When compared with hydrotalcite 2 INVESTIGATIONS (1891À1933) Stichtite was first discovered in western Tasmania, Australia, in 1891; however, it was mistakenly * E-mail: [email protected] identified as ka¨mmererite (a purple form of DOI: 10.1180/claymin.2013.048.4.10 chlorite) at the time by Stitt and Cullingsworth

# 2013 The Mineralogical Society 144 F.L. Theiss et al.

(Twelvetrees, 1914). This mistake occurred because must be the source of Mg2+ as stichtite is always of the remarkable similarity of the two minerals and found intergrown with serpentinite. It is likely that the absence of any chemical analysis. In 1910 the trivalent cations such as Cr3+ (as well as, to a Wesley, the chief chemist at the lesser extent, Al3+ and Fe3+) originate from Mining and Railway Company, Tasmania, (FeCr2O4) as it is present in almost all Australia, conducted the first wet chemical analysis known cases (Ashwal & Cairncross, 1997). No on a sample of stichtite and determined that the individual reaction could be proposed to adequately mineral was not a silicate, as expected, but a new explain stichtite formation; however, stichtite could uncatalogued mineral. Wesley estimated the have formed as a product of the breakdown of empirical formula of the new mineral as serpentinite and chromate by one of two mechan- (CrFe2)O3,6MgO,CO2,13H2O. Stichtite was named isms (Ashwal & Cairncross, 1997): after Robert Carl Sticht, the general manager of the 2 serpentinite + chromite + 8H O+CO ? Mount Lyell Mining and Railway Company, in 2 2 stichtite + 4 quartz + FeO (2) appreciation for his assistance in the preparation of 3 serpentinite + chromite + 7H O+CO ? the ‘Catalogue of the Minerals of Tasmania’. It was 2 2 stichtite + talc + 4 quartz + FeO (3) in this publication by Petterd that stichtite was first reported (Petterd, 1910; Twelvetrees, 1914). Petterd The main problem with the proposed mechanisms was the first to identify the similarity of stichtite to is the absence of quartz, talc or FeO in direct pyroaurite, the iron substituted LDH described association with known stichtite deposits. Ashwal & earlier. Samples of stichtite were sent to the Cairncross suggested this may be explained by the Mineralogic-Petrological Institute in Zurich where dissolution and re-deposition of silica by aqueous Hezner (Twelvetrees, 1914) carried out further and carbonic fluids. FeO may be partially oxidized chemical analysis and confirmed that the sample and form magnetite or removed from solution. The was indeed a new mineral. In a paper published in observation that stichtite usually occurs as veins in 1912, Hezner suggested stichtite may be a chrome- serpentinite deposits provides some evidence to brugnatellite with the formula: 2MgCO35Mg(OH)2 support this mechanism (Ashwal & Cairncross, 2Cr(OH)34H2O. Himmelbauer (Twelvetrees, 1914) 1997). Another possibility is that stichtite may be found that stichtite had a hardness of 1.75 (1¯˘, formed from magnesite or brucite. These equations between gypsum and rock salt), a of do not require the removal of silicates as it would 2.161 (by the fluid method), and a refractive index have occurred during the original formation of the of 1.542 (immersion method). Himmelbauer also magnesite or brucite (Ashwal & Cairncross, 1997). reported the similarity of stichtite to hydrotalcite 6 magnesite + chromite + 12H O ? and pyroaurite in 1913 (Twelvetrees, 1914). The 2 stichtite + 5CO + FeO (4) results described above were translated, compiled 2 6 brucite + chromite + 6H O+CO ? and re-published with the author’s permission by 2 2 stichtite + FeO (5) Twelvetrees for the Tasmanian Department of Mines (Twelvetrees, 1914). By 1933 stichtite had The presence of small amounts of magnesite been identified at three other locations, Black Lake, associated with some stichtite deposits provides Quebec, Canada (1918), the Barberton district, evidence to support this mechanism (Ashwal & Transvaal, South Africa (1922) and the Shetland Cairncross, 1997). Though the exact mechanism of Islands, Scotland (Read, 1933; Mondal & Baidya, stichtite formation is still unclear, the absence of 1996; Ashwal & Cairncross, 1997). silicates associated with stichtite-bearing rocks and the overall rarity of the mineral suggests that a unique combination of conditions must exist for its GEOLOGICAL ORIGIN OF formation. STICHTITE Ashwal and Cairncross performed analysis of SYNTHESIS OF STICHTITE stichtite from various sources in an attempt to understand better the mechanisms of stichtite As previously mentioned, it is difficult to obtain formation (see electron microprobe analysis pure stichtite from natural sources as the material is section below) (Ashwal & Cairncross, 1997). It often intermixed with serpentinites as well as other was clear to Ashwal & Cairncross that serpentinite LDHs including hydrotalcite, pyroaurite, iowaite Stichtite: a review 145

(Mg6 Fe2 Cl2 (OH)16·4H2 O) and reevesite the peak positions in the powder XRD pattern of (Ni6Fe2CO3(OH)16·4H2O) (Twelvetrees, 1914; pink stichtite was investigated. The positions of all Frost & Erickson, 2004). It is therefore necessary reflections in the pattern corresponded to a three- to develop methods for the synthesis of pure layer rhombohedral cell, which is typical of most samples of these minerals to truly understand their carbonate-bearing LDHs (Bookin et al., 1993). To properties and the complex relationship that exists confirm their observations, they attempted to between these LDHs (Frost & Erickson, 2004). simulate the powder XRD pattern of stichtite Frost & Erickson and Bouzaid & Frost prepared using the well established structure of hydrotalcite synthetic stichtite using a variation of the co- (3R1) as a basis for their model. Good agreement precipitation method (Frost & Erickson, 2004; between the major peaks in the model and the Bouzaid & Frost, 2007). This method required the actual powder XRD patterns confirmed that the preparation of two solutions, solution 1 contained pink grains of stichtite were isostructural with NaOH and Na2CO3 (both 2 M). Solution 2 hydrotalcite (3R1) (Bookin et al., 1993). 2+ contained Mg (0.75 M) as Mg(NO3)2·6H2Oand Samples of the green grains did not appear to 3+ Cr (0.25 M)asCrCl3·9H2O. Precipitation of exhibit the same as the pink stichtite occurred when solution 2 was slowly stichtite grains, and did not corresponded to the À1 added to solution 1 at a rate of 40mL min 3R1 structure expected for carbonate-bearing LDHs. under a nitrogen atmosphere and with constant The reflection positions in the pattern corresponded stirring. The resulting precipitate was collected, to a one-layer hexagonal cell (1H) in which a = washed with boiled ultrapure water and dried. 5.3A˚ and c = 7.36A˚ (Bookin et al., 1993). A sample (Frost & Erickson, 2004; Bouzaid & Frost, 2007). of the pink grains exposed to light appeared to Frost and Erickson determined the formula of the contain a combination of both structures. Bookin et synthetic stichtite prepared by this method was al. were able to conclude that the green material Mg5.78Cr2.09CO3(OH)16·4H2O, which is very similar was the product of stichtite decomposition and to the ideal formula of stichtite given earlier. proposed a mechanism to describe this decomposi- tion. It is likely that the green grains described in the paper are a mineral commonly known as POWDER X-RAY DIFFRACTION OF (Mills et al., 2011). STICHTITE Mills et al. (2011) recently re-examined the Powder X-ray diffraction (XRD) is a powerful crystal structure of stichtite and the associated technique that is often used to study crystalline mineral barbertonite using samples of stichtite minerals. Powder XRD of the mineral stichtite was collected from Stichtite Hill, Tasmania, and investigated by Bookin et al. (1993) and Mills et al. barbertonite from Barberton, South Africa. They (2011). Bookin et al. investigated a naturally again showed that the powder XRD pattern of occurring stichtite collected from the Terectin stichtite was dominated by the 3R1 polytype Ridge (Altai Mountains). The stichtite sample common to most LDHs; however, peaks corre- consisted of a mixture of pink and green grains sponding to the 2H1 polytype and lizardite which could be separated with the aid of a (Mg3Si2O5(OH)4) were also observed. The final binocular microscope. Samples of both the pink composition of the sample was and green grains were collected for powder XRD Mg6.12Cr1.88(OH)16(CO3)0.94·4.9H2O, which is analysis. Tatarinov et al. (1985), who originally close to the ideal formula (Mills et al., 2011). studied the sample noted that the pink grains, when Barbertonite is a mineral with the same ideal exposed to X-rays or visible light appeared to chemical formula as stichtite and is described as the undergo a photochemical reaction causing them to hexagonal polymorph of stichtite. It was first change to a green colour. Bookin et al. exposed reported by Fondel (1940) as occurring in some of the pink grains to light over the period of Barberton, South Africa. Powder XRD of barberto- one week to determine if this would be any effect nite showed a material consisting of a mixture of the on the powder XRD pattern of the material. 2H1, and to a lesser extent the 3R1 polytype. Mills et Bookin et al. (1993) reported the interlayer al. (2011) suggested that stichtite and barbertonite distances of the pink and green samples as 7.76 are polymorphs, and as such recommended that and 7.37 A˚ respectively. These values were within barbertonite should be denoted as stichtite-2H in the expected range for an LDH type structure. Next, accordance with Nickel & Grice, 1998. 146 F.L. Theiss et al.

VIBRATIONAL SPECTROSCOPY OF They reported that the n3 antisymmetric stretching STICHTITE mode was present at 1343 cmÀ1. The observed value of the n3 peak is much lower than a typically Frost and Erickson investigated samples of expected value of approximately 1400 cmÀ1. It was synthetic stichtite prepared by the co-precipitation proposed that the n3 peak may be due to the method using infrared (IR), Raman and Near-IR presence of barbertonite impurities in the natural spectroscopy (Frost & Erickson, 2004, 2005). sample (Mills et al., 2011). Numerous bands were identified in the IR spectrum All carbonate modes in the naturally occurring (Frost & Erickson, 2004). A weak band at stichtite were found to be Raman active; this 1076 cmÀ1 that was only observed with 50 times contrasts with the results of Frost and Erickson expansion of the spectrum was attributed to the described earlier. The n1 symmetric carbonate forbidden carbonate symmetric stretching mode. stretching mode was observed at 1055 cmÀ1. The band at 1644 cmÀ1 was attributed to the HOH Asymmetry of this peak suggested the presence of water bending mode. Next, two bands at 1457 and additional unresolved bands. The n2 carbonate À1 À1 1381 cm could be attributed to n3 CO3 stretching mode was present at 680 cm ; antisymmetric stretching modes. Bands at 744 and however, it was extremely weak. The bands at À1 À1 685 cm were assigned to the n4 carbonate 672 and 534 cm were assigned to the n4 bending mode indicating that two carbonate carbonate stretching and n2 carbonate bending species must exist in the interlayer (strongly and a modes respectively (Mills et al., 2011). Bands at weakly bonded). Bands at 909 and 2632 and 2621 cmÀ1 were attributed to Mg-OH and 861 cmÀ1 may be attributed to MOH bending Cr-OH vibrations. It was proposed that these bands modes (where M is Cr or Mg). The hydroxyl may be useful for the identification of stichtite. stretching region IR spectrum was found to result Finally, an additional band at 428 cmÀ1 could only from a complex combination of units including: be attributed to lattice modes (Mills et al., 2011). Mg3OH, Mg2CrOH, MgCr2OH and Cr3OH (Frost & Layered double hydroxides are well suited to Erickson, 2004). Three bands at 3618, 3529 and study by near-IR spectroscopy (NIR) due to the À1 3408 cm could be assigned to the Mg3OH, presence of the hydroxyl surface and interlayer Mg2CrOH and Cr3OH OH stretching bands water. Frost and Erickson investigated synthetic respectively. Two remaining bands at 3220 and stichtite using NIR spectroscopy and found that the 2960 cmÀ1 were assigned to water OH stretching three distinct spectral regions could be observed in (Frost & Erickson, 2004). the NIR spectra of stichtite (Frost & Erickson, Frost and Erickson also carried out Raman 2005). The high wavenumber region microprobe spectroscopy on the same sample of (6400À7400 cmÀ1) was attributed to the first stichtite (Frost & Erickson, 2004). Two intense overtone of the fundamental hydroxyl stretching overlapping bands were observed at 1087 and mode. This region contained a broad profile with À1 À1 1067 cm . These bands were assigned to the n1 inflections at 7200 and 6800 cm . Bands were symmetric carbonate stretching mode. Again two observed at 7246, 7151, 7069, 7017, 6890 and types of carbonate are observed. The band at 6633 cmÀ1 and were attributed to the combination 1087 cmÀ1 couldbeattributedtothestrongly of OH stretching vibrations observed in the mid-IR hydrogen bonded carbonate. The ratio of the region of the spectrum due to the complexity and intensities of the two peaks was calculated to be distribution of the MOH bonds across the LDH. No 2.5:1. This corresponds well to the ratio of 2.3:1 bands could be attributed to specific vibrations in obtained from the corresponding n4 bending mode this spectral region (Frost & Erickson, 2005). peaks at 539 and 531 cmÀ1. The band at 453 cmÀ1 The second spectral region (4800À5400 cmÀ1) was assigned to the CrO stretching mode while the contained the combination modes of the funda- large number of bands between 200 and 366 cmÀ1 mentals of water. Bands were observed at 4460, could only be attributed to lattice modes (Frost & 4411 and 4366 cmÀ1 and attributed to OH Erickson, 2004). combination bands. The third region Mills et al. more recently investigated a naturally (4000À4800 cmÀ1) was attributed to the combina- occurring stichtite using Raman spectroscopy (Mills tion of MOH stretching and deformation modes. et al., 2011). Firstly, no H2O bending bands were Finally, NIR spectra of three different LDH observed in the Raman spectrum of natural stichtite. materials (stichtite, iowaite and desautelsite, Stichtite: a review 147

Mg6Mn2CO3(OH)16·4H2O) were compared. It was Mg6Cr2CO3(OH)16 ? (MgO)6Cr2CO5 +8H2O (5) found that the minerals could be distinguished by (MgO)6Cr2CO5 ? 6MgO + Cr2O3 +CO2 (6) their NIR spectra alone. This demonstrates the MgO + CO2 ? MgCO3 (7) power of NIR spectroscopy as a tool for identifying Cr2O3 +CO2 ? Cr2CO3 (8) and studying LDHs (Frost & Erickson, 2005). Finally the ion current curves revealed the loss of CO and O at 545 and 675ºC. These mass losses THERMAL DECOMPOSITION OF 2 2 were described by the following equations (Bouzaid STICHTITE & Frost, 2007): To our knowledge, thermal decomposition of MgCO ? MgO + CO (9) natural stichtite has never been reported in the 3 2 Cr CO ? Cr O +CO (10) literature. Bouzaid & Frost (2007) used thermo- 2 3 2 3 2 gravimetry coupled with evolved gas mass spectro- metry to determine the mechamism of thermal ELECTRON MICROPROBE decomposition of a sample of synthetic stichtite. ANALYSIS OF STICHTITE Decomposition was found to occur through a mechanism similar to those of most other LDH In an attempt to understand the mineralogy and materials. The first step involved the removal of origin of stichtite better, Ashwal & Cairncross weakly adsorbed and interlayer water at approxi- (1997) carried out electron probe microanalyses on mately 52ºC. Evolved gas mass spectrometry samples of stichtite collected from various locations confirmed the release of H2O, OH and O in this around the world. It was hoped that this technique temperature region. The theoretical mass loss of would reduce interference caused by the numerous water determined from the ideal formula of stichtite impurities present in natural stichtite. Several was 11.0%; however, the mass loss in this unexpected difficulties were encountered and over- temperature region was found to be considerably come before this technique could be successfully greater with a value of 24.9%. It was proposed that applied. As previously mentioned, stichtite is stichtite like some other LDHs (such as honessite, usually intergrown with serpentinite, making it Ni6Fe2SO4(OH)16·4H2O and hydrohonessite, difficult to obtain pure samples. In some specimens Ni6Fe2SO4(OH)16·7H2O) may contain more than the stichtite and serpentinite were too tightly four water molecules per formula unit. Using the intergrown to be resolved even with electron mass loss of 24.9% it was predicted that nine moles probe microanalysis using a highly focused electron of water per formula unit must be present instead of beam (1À2 mm). A reasonable analysis was four (Bouzaid & Frost, 2007). They proposed a obtained by examining spots of the specimens mechanism for the thermal decomposition of with minimal intrusion of silicates using a rapid synthetic stichtite. The first step of the decomposi- energy dispersive analysis technique (Ashwal & tion mechanism can be described by Equation 4 Cairncross, 1997). A second difficulty is that (Bouzaid & Frost, 2007): stichtite volatilises under the normal operating conditions of the electron microprobe used to Mg Cr CO (OH) ·4H O ? 6 2 3 16 2 perform the analyses. To counter this problem, Mg Cr CO (OH) +4HO (4) 6 2 3 16 2 they reduced the beam current to 10 nA (usually The next two steps in the thermal decomposition operated at 15 kV and 15 nA). of stichtite appear to occur almost simultaneously at The electron microprobe analysis was carried out approximately 294ºC. This temperature region on samples collected from the widest range of corresponded to the dehydroxylation and decarbo- stichtite-bearing localities possible. The formulae nation of the stichtite. The ion current curves calculated from all analyses corresponded well to clearly show the loss of H2O, OH and CO2 in this the ideal formula of stichtite. The results obtained temperature region. Ion current curves also show using electron microprobe analysis techniques were that dehydroxylation occurred at a slightly lower much closer to the ideal formula than many results temperature than decarbonation. Equations 5À8 previously reported in the literature. A small but describe the steps that occur in this temperature consistent excess of divalent cations and a similar region during thermal decomposition (Bouzaid & small deficiency of trivalent cations in the layers of Frost, 2007): the LDH suggested that minor substitution of Cr3+ 148 F.L. Theiss et al. with Mg2+ or possible multivalency of ions of Mn Calorimetry, 89, 133À135. or Ni present as impurities occur in stichtite. Frondel C. (1940) Constitution and polymorphism of the Further analysis revealed that that the impurities pyroaurite and sjogrenite groups. Mineralogical often found in a sample of stichtite depend heavily Society of America, Annual Meeting, Program and Abstracts,6À7. on the location from which the sample was Frost R.L. & Erickson K.L. (2004) Vibrational spectro- collected. For example, samples collected from 3+ scopy of stichtite. Spectrochimica Acta Part A: Morocco or India contained more Fe when Molecular and Biomolecular Spectroscopy, 60, compared to samples collected from Russia which 3001À3005. 3+ contain higher levels of Al . The purest stichtites Frost R.L. & Erickson K.L. (2005) Near-infrared were obtained from the Black Lake area in Quebec spectroscopy of stitchtite, iowaite, desautelsite and (Cr > 98 mol.%) with all other samples investigated arsenate exchanged takovite and hydrotalcite. containing more than 15 mol.% hydrotalcite or Spectrochimica Acta Part A: Molecular and pyroaurite (Ashwal & Cairncross, 1997). They Biomolecular Spectroscopy, 61,51À56. concluded that the composition of natural stichtites Frost R.L., Bouzaid J.M. & Martens W.N. (2007) Thermal decomposition of the composite hydrotal- is variable with the exact chemical composition cites of iowaite and woodallite. Journal of Thermal likely depending on the geology of the locality in Analysis and Calorimetry, 89, 511À519. which it is formed. Frost R.L., Palmer S.J. & Spratt H.J. (2009) Thermal decomposition of hydrotalcites with variable cationic CONCLUSIONS ratios. Journal of Thermal Analysis and Calorimetry, 95, 123À129. There have been a number of publications on the Labajos F.M. & Rives V. (1996) Thermal evolution of characterization of natural and synthetic stichtites; chromium(III) ions in hydrotalcite-like compounds. however, there is still much work to be done as the Inorganic Chemistry, 35, 5313À5318. authors were not able to find any publications Mills S.J., Whitfield P.S., Wilson S.A., Woodhouse J.N., Dipple G.M., Raudsepp M. & Francis C.A. (2011) concerning applications of stichtite in the literature. The crystal structure of stichtite, re-examination of Many other LDHs have been investigated for many barbertonite, and the nature of polytypism in MgCr potential applications such as adsorbents, catalysts hydrotalcites. American Mineralogist, 96, 179À187. and polymer additives. It is therefore reasonable to Mondal S.K. & Baidya T.K. (1996) Stichtite expect that stichtite may prove useful for a wide [Mg6Cr2(OH)16 CO3.4H2O] in Nausahi ultramafites, range of applications in the future. Orissa, India; its transformation at elevated tempera- tures. Mineralogical Magazine, 60, 836À840. Nickel E.H. & Grice J.D. (1998) The IMA Commission ACKNOWLEDGMENTS on New Minerals and Mineral Names: Procedures and guidelines on mineral nomenclature, 1998. The financial and infra-structure support of the Discipline Mineralogy and Petrology, 64, 237À263. of Nanotechnology and Molecular Science and the School Petterd W.F. (1910) Catalogue of the Minerals of of Chemistry, Physics and Mechanical Engineering of the Tasmania. Tasmania Department of Mines. Faculty of Science and Engineering, Queensland Read H.H. (1933) On stichtite from Cunningsburgh, University of Technology, is gratefully acknowledged. Shetland Islands. Mineralogical Magazine, 23, 309À316. Rives V. (2001) Layered Double Hydroxides: Present REFERENCES and Future. Nova Science Publ. Inc., New York. Ashwal L.D. & Cairncross B. (1997) Mineralogy and Rives V. (2002) Characterisation of layered double origin of stichtite in chromite-bearing serpentinites. hydroxides and their decomposition products. Contributions to Mineralogy and Petrology, 127, Materials Chemistry and Physics, 75,19À25. 75À86. Tatarinov A.V., Sapozhnikov A.N., Prokudin S. & Bookin A.S., Cherkashin V.I. & Drits V.A. (1993) Frolova L.P. (1985) Stichtite in serpentinites of Reinterpretation of the X-ray diffraction patterns of Terektinsky Ridge (Mountain Altay). Zapiski RMO stichtite and reevesite. Clays and Clay Minerals, 41, (Proceedings of the Russian Mineralogical Society), 631À634. 114, 575À581. Bouzaid J. & Frost R.L. (2007) Thermal decomposition Twelvetrees W.H. (1914) Stichtite: a New Tasmanian of stichtite. Journal of Thermal Analysis and Mineral. Tasmania Department of Mines.