ON ROZENITEAND SIDEROTIL J. L. JAMBORexo R. J. TRAILL GeologbalSurvey of Canad,a.,Ottawa AssrRAcr Melanterite, FeSOr.THzO, from Manitoba, Canada, dehydrates to FeSOr.4HzO whichismonoclinic,a: 5.945,b: 13.59,c :7.g44,F : g0'30'.Cuprianmelanterites, or pisanites, (Fe,Cu)SOa.7HrO, dehydrate to a pentahydrate series.A naturally occurring pentahydrate from Yerington, Nevada, contains FeO 15.9/6, CuO 14.1, CoO 0.35, SOa 32.99 (by difference), H2O 36.66. Such pentahydrates are biaxial negative with 2V - 50-65", a - 1.513, I - L.526, - 1.536,whereas FeSOa.4HrO is biaxial negative with a very Larye 2V and a-t,526," g -1.536, "y-t.545. Examination of previously published data shows that "iron-copper chalcanthite" is cuprian FeSOr. SH:O and that compilations have attributed optical data determined on FeSOn,4HrO as belonging to FeSOr.SHzO. Indexed r-ray powder data for FeSOa.4HzO and cuprian FeSOa.SHrO are given. The strongest lines of the powder pattern ol the tetrahydrate are 4.47(10),5.46(9), 3.97(7),3.40(6), 6.85(5), and the stiongest lines for the pentahydrate are 4.89(10), 3.73(8),5.57(6), 5.73(5). Synthesis of the ferroan CuSOn.SHIOand cuprian FeSOa.SHeO series is described and the nomenclature of the pentahydrates and tetrahydrates is discussed.The present writers prefer to retain the mineral names and chemical com- positions as originally defined: FeSOa.SHzO : siderotil: FeSOa.4HgO : rozenite. INrnoouctron Textbooks on optical and descriptive mineralogy state that melanterite, FeSOa.THgO,alters by dehydration to form the mineral siderotil having tJle compositionFeSOq.5HrO. Rosenzweig & Gross (1955)and Kubisz (1960)have found that melanterite dehydrates to form the tetrahydrate, FeSOa.4HsO,which Kubisz has named rozenite.On reviewingthe pub- lished new name Fleischer (1961) pointed out that the optical properties of rozenite are identical to those given for siderotil in Dana (Palache, Berman & Frondel, 1951).Noting also that the original chemicalanalysis of siderotil by Schrauf (1891) was not conclusive, Fleischer suggested that rozenite was an unnecessaryname and that siderotil should be used for the tetrahydrate. Midgley (1962) has followed Fleischer'ssuggestion and referred to the tetrahydrate as siderotil. On the other hand, Baur (1962)prefers to discreditsiderotil and retain rozenitefor the tetrahydrate. The present problem of nomenclature originated from an inadequate descriptionby Schrauf (1391)of the mineral which he named siderotil. Confusion beganwhen Larsen & Glenn (1920)assigned optical properties to a supposedly similar mineral and was perpetuated by compilers of data, namely Larsen& Berman (1934),Winchell & Winchell (1956)and Palache et al,. (L95L).These writers combined the name siderotil, having IDL Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/7/5/751/4005046/751_7_5_cm.pdf by guest on 01 October 2021 752 THE CANADIAN MINERALOGIST Schrauf's composition FeSOa.5H2O, with optical properties which were determined some 30 years later by Larsen & Glenn on unanalyzed materials not from the type locality. The description of rozenite by Kubisz (1960) contains sufficient data to clearly characterize the tetrahydrate mineral (FeSOe.4HzO) and thus constitutes a valid description of a mineral that previously had been neither adequately described nor properly named. Unfortunately, Kubisz did not discuss the relationship of his mineral to siderotil (as FeSOn. 5HrO). Neither Fleischer nor Midgley has recognized that the pentahydrate FeSOn.5HrO, and particularly the cuprian variety, (Fe,Cu)SOa.5HzO, may occur in nature and are probably more deserving of the name side- rotil than the tetrahydrate. The present writers favour use of the name rozenite for the tetrahydrate (Kubisz, 1960) and propose that siderotil be used for the pentahydrate, thus fulfilling the suggestion that Schrauf (1891) expressed in the following words: "Hieraus wtirde sich die Formel der Verbindung zu FeSOa. 5HzO berechnen. Solten fernere Beobachtungen die Existenz eines solchen strahligen vrasserarmen Ferrosulphates bestdtigen, so wiirde ich den Namen Siderotil hiefiir vorschlagen." Recent studies of the tetrahydrate have shown that many properties previously described for the pentahydrate "siderotil" are really those of the tetrahydrate. In the present paper, the dehydration of the hepta- hydrate, melanterite, is discussed and properties are given for the tetra- hydrate and pentahydrate minerals that may form. Previously published data are re-examined with regard to these properties, and the proposed nomenclature is discussed. Tne DBnnoRATIoN oF MELANTERTTE In 1960, the first author examined a white mineral associated with melanterite on a specimen from Manitoba, Canada, and found that it gave an x-ray difrnction pattern in close agreement with that of the artificial compound FeSOa.4H:O. On exposure to air for several hours at 22" C. and 50 per cent relative humidity, the melanterite dehydrated to form a white powdery coating which, on tc-ray examination, proved to be the tetrahydrate. It was then shown conclusively by means of a thermo- gravimetric apparatus that the melanterite from Manitoba dehydrates directly to the tetrahydrate at 2I" C. without forming an intervening pentahydrate phase. This evidence is in conflict with the statement of Larsen & Glenn (1920), subsequently repeated in many textbooks, that "Melanterite is commonly coated with a white powder of siderotil and the fine [melanterite] powder will dehydrate after standing for some months to the pentahydrate." It is now known that this white powder Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/7/5/751/4005046/751_7_5_cm.pdf by guest on 01 October 2021 ROZENITEAND SIDEROTIL 753 was not a pentahydrate, but was a tetrahydrate, and herein the confusion began. Larsen & Glenn gave, for this white tetrahydrate powder, optical properties which have been repeatedly and erroneously attributed, via compilations, as being those of the pentahydrate. Palache, Berman & Frondel (1951) have pointed out that in the arti- ficial system the tetrahydrate is ordinarily formed by dehydration of tJre heptahydrate, and Rosenzweig & Gross (1955) have noted that melan- terite dehydrates rapidly to FeSOa.4HzO; the latter authors, however, did not present any evidence to support the statement. The study of the dehydration of melanterite from Manitoba and description of the tetra- hydrate mineral were not published when Kubisz (1960) presented details of an almost identical study on melanterite from the "Staszic" mine, Rudki, Poland. The fact that melanterite forms a tetrahydrate upon dehydration no longer applies when the melanterite contains minor amounts of copper in substitution for iron. Eckel (1933) studied the stability relations of a cuprian melanterite (pisanite) containing 7.2 per cent CuO. Eckel's experimental method was to allow weighed samples to come to equili- brium in artificially-produced atmospheres of known humidity. Abrupt changes in weight were found to occur at three points, the lossesin weight corresponding closely to the removal of a definite number of molecules of water of crystallization. These abrupt changes marked the following dehydration stages: (Fe,Cu)SOa.7H2O -+ (Fe,Cu)SOa. 5H20 --+(Fe,Cu)SOa . HzO -+anhydrous. No indication of a tetrahydrate phase was found. A naturally occurring counterpart of Eckel's cuprian iron sulphate pentahydrate has been examined by tJle writers. The specimen, labelled "Pisanite, Yerington, Nevada" was received from tJre Royal Ontario Museum in a stoppered glass vial sealed with wax. Chemical analysis of the mineral (Table 5) shows that its formula is (Fee.s6Cuo.oa Coo.or) SOa.5HzO. The mineral consists of sub-fibrous grains that are consider- ably coarser than the tiny anhedral or fibrous grains, or porous aggre- gates that are generally characteristic of minerals formed by dehydration. The grain size and texture of tJle Yerington cuprian iron sulphate penta- hydrate suggest that it may not have been formed by dehydration of cuprian melanterite but may have been precipitated from solution. PnopBntres on FeSOn. 4HsO P hy s'ical, and Opti,cal, Pr op ert'ies FeSOa.4HsO is white to greenish white with a vitreous lustre and white streak. The mineral commonly forms by dehydration of the higher Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/7/5/751/4005046/751_7_5_cm.pdf by guest on 01 October 2021 754 TgE cANADTAN MINERALocIST hydrate and its fine-grained nature makes difficult the accurate deter- mination of its physical and optical properties.Contrary to the statement of Midgley (1962,p. 408), the tetrahydrate (and not melanterite) is the stable phase at normal temperatures and humidities. Some oxidation of iron takes place producing a yellowish colouration but the water content remains unchanged. Kubisz (1960)reports a measuredspecific gravity of.2.195for rozenite. This figure is lower than the range 2.23-2.29 given for FeSOa'4HzOin the Handbook of Chemistry and Physics.The calculated specificgravity is2.29, basedon the crystallographic constantsof Baur (1960). Optical properties of the tetrahydrate are given in Table L. The properties listed in columns I, II and III were determined on minerals that had been positively identified by x-ray powder diffraction patterns. Tesln L. OErrcar- Psopnntrss op FeSOr4HzO II III IV VI e L.527 L.527* 1.529x t.526 r..528 1.528 B 1.536 1.536 t.537 1.537 "yI.54L* l".543* l".543r' L.542 t.545 L.545 slgn (-) (-) (-) (-) (-) 2V near 90o near 90" rather rather moderate large large *Constants ^y' determined as'lp. a' or I Manitoba mineral; M, R. 28, W. of lst meridian. II Rozenite from Staszic (Kubisz, 1960). III Rozenite from Ornak (Kubisz, 1960). IV "Siderotil" from dehydration of melanterite (Larsen & Glenn' 1920)' V "Siderotil" from California (Larsen, 1921). VI "FeSOa.5HrO," synthetic (Winchell, 1927). Chemical analysesfor I and II are given in Table 2. The properties listed in columns IV, V and VI are also those of the tetrahydrate, but in each casetJrey presumably have been incorrectly reported in the literature as belonging to the pentahydrate.