Glaucochroite(Olivine, Camnsioo) from Franklin, New Jersey: Its Composition,Occurrence, and Formation Prrnn B
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American Mineralogist, Volume 72, pages423-428, 1987 Glaucochroite(olivine, CaMnSiOo) from Franklin, New Jersey: Its composition,occurrence, and formation Prrnn B. Ln,c,vnNs Department of Geology, University of Delaware,Newark, Delaware 19716, U.S.A. Prrn J. DUNN Department of Mineral Sciences,Smithsonian Institution, Washington,D.C. 20560, U.S.A. DoNu,n M. Bunr Department of Geology, Arizona State University, Tempe, Arizona 85287, U.S.A. Ansruct Glaucochroite, CaMnSiOo,is a member of the olivine group, known primarily from the Zn-Mn-Fe deposit at Franklin, New Jersey.Euhedral crystalsoccur in a number of assem- blageswith nasonite,willemite, clinohedrite, hardystonite, diopside, and cuspidine. Mas- sive, coarse-grained,blue glaucochroiteoccurs with willemite, franklinite, calcite, hardy- stonite, leucophoenicite,and andradite. Massive, fine-grainedbrown glaucochroiteoccurs with esperite, hodgkinsonite, calcite, willemite, zincite, and franklinite, and as "calc- tephroite," an inhomogeneous,sheared or altered material. Glaucochroite was not ob- served in association with tephroite, rhodonite, or wollastonite, all of which occur at Franklin. Fourteen glaucochroiteanalyses conform closely to the ideal formula, with little solid solution toward tephroite. Glaucochroite can form either by the heterogeneousreaction calcite + bustamite + tephroite : glaucochroite + CO, or by gradual extensionof olivine composition from tephroite to glaucochroiteabove the olivine solvus. At Franklin, glau- cochroite is interpreted as forming instead of the commoner assemblagerhodonite + calcite in local areas with high activity of water and low activity of carbon dioxide, but under the same temperature and pressrueconditions as the deposit as a whole. Cuspidine, CauSirO?(F,OH)r,is here confirmed as occurring at Franklin. It occurs with glaucochoiteand hardystonite,and in solution vugs in willemite. Two microprobe analyses averagedSiO, 32.6, CaO 62.3,F 9.7, lessO : F 4.1, total 100.5wt0/0, conforming closely to the ideal composition. hvrnooucrroN The deposit has been highly deformed and metamor- Glaucochroite, CaMnSiOr, was described by Penfield phosed at temperatures of at least 650-750'C (Frondel and Warren (1899) as minute blue crystals embeddedin and Klein, 1965) and pressuresofseveral kilobars, based nasonite from the Franklin, SussexCounty, New Jersey, on the geology of the surrounding rocks (Hague et al., Zn-Fe-Mn deposit. Palache(1935) describedglaucochro- l 956). ite in "a coarsegranular form of bluish color, intimately The Franklin mine closedin 1954 and is now flooded. mixed with willemite, hardystonite,tephroite, and frank- Assemblagescan only be studied in hand specimens,most linite." More recently, glaucochroitehas been found in a lacking reference to location or petrologic relationships. skarn formed at the contact betweendolerite and marble There are a number of referencesto glaucochroite on the in Anakit, Lower Tunguska, USSR (Pertsev and Lapu- minelevel maps, which suggestthat it was widely dis- tina, 1974), and in calc-silicate rocks associated with tributed in the northern parts of the mine. manganeseoxide ores in the Wesselsmine, South Africa (R. D. Dixon, pers. comm.). Eunronlr, cRysrAr,s oF GLAUcocHRorrE The initial discovery of glaucochroite (Penfield and Occunnnxcn Warren, 1899)was of euhedralcrystals collected from the Frondel and Baum (1974) describedthe structure and dump of the Parker shaft near the end of the last century, mineralogy of the Franklin deposit, basedon level maps with other rare minerals, including nasonite and other of the mine prepared during mining operations. The de- lead silicates.Because the preservedsamples ofeuhedral posit is a complex metasedimentaryunit containing both glaucochroite are few in number and their parageneses Zn-ich ore units and Zn-poor calcium silicate skarns. are only generally in agreement with the original descrip- 0003-004V87/030,t4423$02.00 423 424 LEAVENS ET AL.: GLAUCOCHROITE (OLIVINE, CaMnSiO.) tion and that ofPalache (1935), we gatheredtogether the ported from Franklin by Palache(1910, 1935)as a result l5 available specimensof glaucochroitecrystals, and they of his interpretation of an 1899 analysisby C. H. Warren permitted the recognition of severaldistinct assemblages: of colorlesscrystals associated with nasonite,but samples l. Glaucochroite occurs embedded in nasonite, of this material have been unknown since then. Cuspi- PbuCaoSiuO,Clr,with minor amounts of primary frank- dine forms colorless,clear, distorted crystals.The density linite and andradite, and abundant light-yellow andra- is between 2.965 and 2.989 (Palache,l9l0). Franklin dite, which surrounds the primary material. Presentonly cuspidine is readily recognizedby its moderately strong in very minor amounts are barite, clinohedite, CaZn- yellow-toJight violet fluorescencein long-wavelengthul- SiO3(OH)r,willemite, and a late-stageMn-chlorite traviolet. The fluorescencein short-wavelength ultravi- (NMNH B2r24t, C2799). olet is similar, but weaker. Cuspidine, like glaucochroite, 2. Glaucochroite occurs embedded in massive green has not been found at Sterling Hill. willemite that encrusts common, granular willemite- Microprobe analysesof Franklin cuspidine, which are franklinite ore. Both andradite and hodgkinsonite, in reasonablygood agreementwith that of Warren, yield- MnZnrSiOo(OH)r, form at the interface between the ore ed SiO, 32.3,32.8; CaO 63.5,6 I . l; F 9.8, 9.5;less O : and the green willemite, suggestinga vein assemblage. F 4 .l , 4.0; totals 10 I .5, 99.4 wto/oand conform closely to Clinohedrite intergrown with the willemite has a vuggy the ideal composition. Substitution of (OH) for F is min- texture suggesting later crystallization. Cuspidine occu- imal in Franklin cuspidine. Cuspidine is in apparent pies solution vugs in willemite. Barite is presentin minor chemical equilibrium with glaucochroite,which is youn- amounrs. (NMNH 821402.) ger, and hardystonite,which is altered in some specimens 3. Massive, white clinohedrite occurs associatedwith to clinohedrite. Cuspidine also occurs, within assem- andradite and hardystonite, CarZnSirOr. Glaucochroite blages of glaucochroite crystals, as a late-stagemineral, crystals occur within both hardystonite and clinohedrite. forming druseswith clinohedrite in solution vugs in wil- Andradite of several generations is present, encloses lemite. franklinite (sparse),and is older than the hardystonite + clinohedrite * glaucochroite assemblage.Some speci- Mlssn'n cLAUcocHRorrE mens have a brecciaJike texture wherein garnet is ce- In the ores and calc-silicate rocks, several different mented with the glaucochroite-bearingassemblage. Cus- massive glaucochroite-bearingassemblages may be dis- pidine is present on two specimens,in 2-3-mm crystals, tinguished. On the basis of textures of hand specimens, and in apparent chemical equilibrium with the glau- there are four assemblagescontaining coarse-grainedblue cochroiteassemblage. (NMNH 93032, I13684, C2798.) glaucochroite and two containing fine-grained brown 4. Massive willemite occurs with 1.0-cm white diop- glaucochroite.The coarse-grainedassemblages are as fol- side crystals, and slightly pinkish-blue massive glau- lows: cochroite. Clinohedrite, nonfluorescentcalcite, and stilp- l. Bright-green willemite, blue glaucochroite, and nomelane are minor phases.This assemblageis wggy, franklinite, occur in octahedra up to 2 cm. All three species and euhedral glaucochroitecrystals line the vugs. are always present;hardystonite and calcite are common In most of these assemblages,glaucochroite forms but not always present. Leucophoenicite, (Mn,Zn)t- bladed crystalsup to I cm in length, frequently in colum- Si3O,r(OH), and zincite are sparse. (NMNH 138406, nar bundles. AssemblageI was that originally described 138407,144684,R3494, and othersin the Harvard and by Penfieldand Warren (1899).Assemblages 2 and 3 were Delaware collections.) apparently known to Palache (1935), but not described 2. Blue glaucochroiteoccurs with willemite and frank- in detail. Assemblage3 was found in the Yale University linite and leucophoenicite.Hardystonite and calcite are collection; the labels were in Penfield's handwriting, and absent or present only in traces. One specimen of the the samples are undoubtedly from the turn-of-the-cen- assemblage(JEM 3107) shows in hand specimen blue tury finds. The axinite reported by previous investigators glaucochroite grading into pink leucophoenicite over a in this associationis probably andradite. distance of about 4 cm in a matrix of gneissicfranklinite The associationof the high-temperaturemineral glau- with minor willemite and sparsenative copper. Average cochroite with clinohedrite is anomalous,as clinohedrite grain size is about l-3 mm. In thin section,the specimen is typical of altered and recrystallizedassemblages. It fre- shows a granoblastic texture ofthe glaucochroite,leuco- quently forms from hydrothermal alteration of hardy- phoenicite, and willemite, suggestingan equilibrium in- stonite, a member of the melilite group. However, several tergowth of glaucochroite and leucophoenicite rather than samples show that the association of euhedral glau- replacement of one by the other. (NMNH 107374, cochroite crystals with clinohedrite results from the al- 147244,C6172, R6602.) teration of hardystonite, the primary host for elauco- 3. Andradite, willemite, glaucochroite,and calcite oc- chroite, to clinohedrite, particularly in assemblage3. cur in a coarse granular intergrowth. This assernblagewas seenin