American Mineralogist, Volume64, pages 367-36g, 1979

Newdata on cerianvesuvianite from san Benitocounty, california

Wu-soNW. Cnoor, III nNnSreulry G. Oswelo Mobil Oil Corporation,P.O. Box 5444 Denuer.Colorado 80217

Abstract

A previously-reported cerium-rich vesuvianitefrom San Benito County, California, was re- investigated using powder diffraction, single-crystal X-ray, and electron microprobe tech- niques. The material was shown to be a variety of vesuvianite with space group p4/nnc, a : 15.631-15.932,c=11.858-11.8964,2:4.Uniaxialnegative,e:1.723-1.756,o::1.741- : 1.763.Gmeas 3.564-4.074.Chemical analysesshow the mineral to correspondto a general- ized vesuvianite formula, (Ca,RE),r_"(Mg,Fes+,Mn,Ti,Al)1sysir8(O,OH),u, with slight site deficienciesdue to the presenceof abundant rare-earths.

Introduction The mineralis uniaxial(-)with e :1.732(2),ot: Cerian vesuvianitewas originally reported from 1.741(2)(red to gold color,RE-poor); e : 1.756(2),a : San Benito County, California by Murdoch and ln- 1.762(2)(black color, RE-rich) (Na light). Atl gram in 1966.Due to the lack of quantitative chem- grains examinedare non-pleochroic. ical data on the individual rare-earthelements, it was suggestedto the authors by Delbert L. Oswald, head X-ray crystallography of the mineralogy department at the Carnegie Mu- Single crystalswere studied using oscillatingcrys- seum of Natural History, that the mineral be re- tal, Weissenberg,and precessionmethods. Unit-cell investigatedusing electron microprobe analysis.Sub- parameters from a least-squaresrefinement are a : sequentchemical, physical, X-ray single-crystal,and 15.631(2),c : I 1.858(l)(RE-poor); a : 15.932(3),c powder data confirm the generalconclusions reached : 11.896(l)(RE-rich), V : 2897.2-3019.543,Z : 4. by Murdoch and Ingram. Extinctions observedwere: {0kl}, k + I : 2n -t l; -t The mineral occurs on fractures in extremely al- th04, h I : 2n + l; lhk}l,k = 2n * l. The space teredgreenstones of Franciscanage. Associated min- group is P4/nnc. erals include melanite garnet, chlorite, diopside, clinozoisite,perovskite, and apatite.Cerian vesuvian- Chemical analysis ite is easily distinguishedby its characteristicpris- An electron microprobe analysis (Table l), con- matic habit and gold to brown-black color. ducted with 150 nA specimen current and 15 kV excitationvoltage, was usedin the characterizationof Physical properties cerian vesuvianite.Water was measured by weight Cerian vesuvianite occurs as slender prismatic losson ignition. The iron is assumedto be presentas (0.2-3.0 mm) crystals with observed forms {010}, Fe3+,because this is the valenceof iron reported in {001i,{ll0}, {l0l}, {lll}, and {12l}.Fracture is sub- the originally describedmaterial (Murdoch and In- conchoidal,and there is no observablecleavage. The gram, 1966). Corrections were made using the Eu- color is variable from translucentgold to deepred to pnon VII program of Rucklidge and Gasparrini an opaque brown-black, the intensity of the color (r e69). increasingwith increasingRE content. The streak is Electron microprobe analyseswere normalized to white, and the hardnessis 5Vz-6V2.The speciflcgrav- 76 total O + OH, consistent with the generalized ity (21'C) was determined on a Berman balanceby vesuvianiteformula, ArcBrcCB(O,OH,F)?6.There is a repeated measurementson single crystals weighing great deal of substitution in the A and I sites such l2-18 mg to be 4.074(5)on opaqueRE-rich material, that the chemical formula for the RE-rich material and 3.564(5)-3.829(5)on gold to red specimens. (analysis l) is (Carr665Na6.12sK6.1rrYoonrLao..rrCerrru 0003-004x/79/0304-0367$02.00 xt 368 CROOK AND OSWALD: CERIAN VESUVIANITE

Table l. Chemical analysisof cerian vesuvianite Sirs(O,OH)?..The presenceof abundant rare earths (20.57 weight percent) accounts for the slight site T2 EzO3 L 2 deficienciesseen in both the A and B sites. CaO 22.45 3r.06 La2o3 3.47 0.43 Discussion Na2O 0, 15 0.26 Ce2O3 6 .09 l. I8 Thesedata suggestthat the mineral is a rare-earth, Kzo Pr2o3 1.39 0.29 0. 19 0, 19 notably cerium-rich variety of vesuvianite.Optical m203 20.57 4.87 Nd2o3 2.04 0.61 and physicaldata are slightly differentfrom reported M9o Sn2O3 2,98 0.88 valuesfor vesuvianite,but are not unreasonablecon- sidering the substitution of the rare-earthsfor cal- Fero, 3.05 5.51 Gd2o3 1.04 0.14 cium. X-ray data show the mineral to have space MnO 0.29 0.62 Tb2o3 o .26 0.03 group P4/n/?c,consistent with known vesuvianites, TiO2 2.47 4.08 DyZo3 0.94 0.25 with an expanded lattice due to the increasingRE AI2O3 10.87 11.58 Ho2o3 O.23 0.15 content. Chemical analysesof all color types show a range in total RE content from 0.64 to 20.57weight sio2 5J.)b 5>.tl Er2o3 0.29 0. 12 percent. Previously-reportedRE vesuvianites(Orlov Hza 2.r7 1.86 Ttn2O3 0.05 0.04 and Mart'yanov, 196l; Murdoch and Ingram, 1966) Yb2O3 o'rt 0.22 list valueswhich fit into this range but do not exceed

Lu2o3 0.I2 0. 18 ir.

v n 1 Eq n ?R z5 References

99.69 99.27 suM 20.57 4.87 Murdoch, J. and B. L. Ingram (1966)A cerian vesuvianitefrom California. Am. Mineral., J1, 381-387. I. Rare-earth-rich vesuvianite, San Benito Co. Orlov, Y. L. and N. N Mart'yanov (1961)Vesuvianite, containing rare earth elements from the Ensei Mountain Range. Tnuty Rare-earth-poor vesuvianite, San Benito Co. Mineralog. Muz. Akad. Nauk SSSR, I I, 187. Rucklidge, J C and E. L Casparrini (1969) Specifcations of a Complete Program for Processing Electron Microprobe Data: Pro Ndo r.nSm o ur.Gd o.rnzTbo.oo. DYo r' Hoo on.Ero on, "rr EMPADR Z1l Departmentof Geology, Universityof Toronto. Tmo orrYboo2lLuo.orr)(Mgr touFeiSrzMno 128Tio rrrAl..tto) (Sirr.r.oAlo.1roXO.r..r.OHr6r.). Thus the idealized Manuscripl. receiued,June 15, 1978; formula is (Ca,RE)'n-,(Mg,Fe3+,Mn,Ti,Al)'r-n acceptedlor publication, September 2, 1978