American Mineralogist, Volume 62, pages 416420, 1977 Zektzerite: a new lithium sodiumzirconium silicate related to tuhualiteand the osumilitegroup Pprr J. DUNN Department of Mineral Sciences SmithsonianInstitution, Washington,D.C. 20560 RollNn C. Rousn Department of Geology, Uniuersity oJ Michigan Ann Arbor, M ichigan 48 I 09 Bnnr CeNNoN Cordilleran, l8 Holly Hill Driue M erc er I sland, Washingt on, 98040 JosepsA. NBr-aN Department of Mineral Sciences SmithsonianInstitution, Washington,D.C. 20560 Abstract Zektzerite,LiNa(Zr,Ti,Hf)Si6O,u, is a new mineral speciesoccuring as colorlessto pink euhedralcrystals in a riebeckitegranite from OkanoganCounty, Washington. It is ortho- rhombic, Cmca or C2ca, with a : 14.306(5),b : 17.330(4),c = 10.140(3)A,Z : 8. The strongestreflections (in A) in theX-ray powderpattern are 7.190 78 200;4.850 100 221;4.336 78 040; 3.48075 241; 3.14585 023,421;and 2.66565 043,441.Physical properties include perfectcleavages on {100}and {010}, white streak, vitreous luster, Mohs hardness about 6, and densityof 2.79g/cm'. Optically,zektzerite is biaxialnegative, almost isotropic, with2V, : -0o. Indicesared:1.582(3),8: 1.584(3),and7:1.584(3)withorientationX: a,Y: b, and Z : c. Dispersionis very weak, r ) u. Zektzeriteis closely relatedto tuhualite, (Na,K)rFe?+Fe!+Si,rO3o.H2O,and more distantly to the osumilitegroup. Introduction to publication.Holotype material is depositedin the It is quiteuncommon in contemporarymineralogy National Museumof Natural History, Smithsonian to encountera new mineral occurringin euhedral Institution,Washington, D.C., undercatalog #136030. crystalsup to 35 mm in sizeand sufficientlypure to Cotype materialhas beendeposited in the British enablea relativelyfacile characterization.Such a Museum(Natural History),London, England. mineralwas found by oneof theauthors (BC) in 1968 and wassent to the SmithsonianInstitution in 1975 Occurrenceand local geology by Mr. JackZektzer, of Seattle,Washington. A de- Zeklzeriteoccurs in the Golden Horn batholith of tailed investigationhas confirmedthat it is a new Eoceneage, near WashingtonPass,, in southwestern species,which we have named zektzeite after Mr. OkanoganCounty, Washington,at elevationsbe- Zektzerin recognitionof his initiationof this effort. tween4600' and 7400'(lat 48o32'N, long. 120'35' The new nameis pronouncedzex'-ter-ite. The min- W). The intrusionhas invaded Cretaceous metamor- eraland the namewere approved by theCommission phicand igneous rocks and is now exposedthrough a on New Mineralsand MineralNames, I.M.A., prior total reliefof 5300'over an areaof 120square miles 4t6 DUNN ET AL.: ZEKTZERITE 417 withinthe ruggedlandscape of the NorthernCascade thermalalteration in all phasesof the batholithhas Mountains(R. T. Stull, unpublishedthesis, 1969). left many pocketswithin the affectedzones stripped The batholithexists in threecompositional phases. of all mineralsbut quafiz and feldspar.Magnetite, The oldest phase hosts the zektzerite and is a rie- fluorite, and siderite,usually altered to hydrousiron beckitegranite consisting of quartz,riebeckite, and oxides,have beensubsequently deposited in some perthite. It commonlydisplays miarolitic and grano- pockets. phyric texturosand is believedto havecrystallized at physicalproperties a shallowdepth at pressuresbetween 0.5 and 1.0kbar Morphology,optical and (Stull,1973). Calcium and magnesiumare nearly ab- Zektzeriteoccurs as euhedralcrystals up to 37 mm sent,and aluminumis presentin quantitiesslightly X 35 mm X l5 mm, andsome are lightly coated with belowthat of a normalgranite. The lithium content, an iron oxide film. The crystalsare orthorhombic, however,is somewhathigher (a2 ppm) thanthat of a pseudohexagonal,and the morphologysuggests the typicalgranite, and the riebeckitemay containup to class2/m 2/m 2/m. the dominantforms are {100}, 1290ppm lithium. {010},and {011},and most of thecrystals are tabular The remainingphases in the batholith are more on {100}.There is a pearlyluster on {100},and {01l} is normalgranites containing biotite, hastingsite, horn- lightlystriated parallel to a. A sketchof an idealized blende,plagioclase, orthoclase, and quartz.They are crystalof zektzeriteis shownin Figure 1,and a sketch thoughtto havebeen derived from the alkalinegran- of zektzeriteon riebeckitein Figure2. ite throughthe incorporationof dioriticxenoliths (R. Zektzeritecrystals are colorlessto pink, have a J. Stull,unpublished thesis, 1969). white streak,and may exhibit color zoning.Many Zektzeritehas beenfound in lessthan fifty miaro- crystalsshow translucentinteriors which are pink, litic cavitiesoccurring both in situ and in talusboul- colorless,or cream-colored,and which are sur- dersalong a narrowthree mile belt in the riebeckite roundedby a whitishchatoyant zone l-2 mm thick granite.Thousands of additionalpockets examined on prism and pinacoidfaces. There are cleavages by Cannon and others (Jack Zektzer, and Russell, parallelto {100}and {010},both perfectand easily Robert,and John Boggs)in a fourteensquare-mile areawere found to containno crystalsof the new mineral.Zektzerite-bearing pockets are usually small, from 2 to l0 cm in their longestdimension, are clay- free and with walls still attachedto their enclosing rock.Typical zektzerite crystals are from 4 to l5 mm in diameterand occurseveral to a pocket,loose or scatteredupon whitemicrocline and associatedwith lustroussmoky quartz crystals up to 6 cm long,well- formed riebeckitecrystals up to 3 cm long, and tiny euhedralzircon crystals. Astrophyllite, elpidite, and acmiteare also found as associatedminerals in the miaroliticcavities. Unusual pockets may yieldover a dozenzeklzerite crystals ranging in sizeup to 2.5cm. Two exceptionalcylindrical-shaped pockets, one 2l X 12cm andthe other42 X 9 cm,had collapsed walls showingsecondary qvaftz growing upon the separa- tion surfaces,and yieldedabout 50 zektzeritecrystals, mostlyunder l2 mm. Thepocket of the typematerial wasrelatively small (about I I X 5 cm) but contained a slightly etchedcrystal 3.7 X 3.5 X 1.5 cm, the largestone yet found. Zektzerite-barrenpockets within the riebeckite granitemay be more than 26 cm in diameterand contain,in addition to the mineralsalready men- tioned,chlorite, sericite, calcite, fluorite, and rarely Fig. l. Idealizeddrawing of a typicalzektzerite crystal. (drawing allanite,stilbite, bastnaesite, and loellingite.Hydro- by BartCannon) 4t8 DUNN ET AL.: ZEKTZERITE analysisindicated the absenceof other elementsex- cept in trace amounts. Water, as determined by the Penfieldmethod, on 300 mg., is absent.The resultsof the analysis of zektzerite are presentedin Table l. From the analysis, the calculated formula is Lir.ooNar.or(Zro.rnTio.ouHfo.ol)Si6060ruru, which agrees very well with the ideal LiNaZrSi.Olu. X-ray crystallography Precessionph otographs of zeklzerirei ndicated that the mineral is orthorhombic, space group C2ca or Cmca, with approximate unit-cell parameters a : 14.3. b : 17.4. and c : 10.2A. These translations were then verified by means of overexposedcone-axis o,r rotation photographs around each axis. Using powder-diffractometer data gathered with mono- chromatized CuKa radiation and quartz (a Fig. 2. Sketch of zektzerite on riebeckite. Scale-bar is I cm. 4.9133,c = 5.4049A)as an internal standard,a least- (sketchby Bart Cannon) squaresrefinement of the above parametersyielded produced. The luster on cleavagesurfaces and frac- the valuesa : 14.306esd0.005, b : 17.330esd0.0O4, ture surfacesis vitreous. The Mohs hardnessis about and c : 10.140esd 0.0034. The unit-cellvolume is six. The density, measuredon a Berman balance in 2514.0 esd 0.9A", and the axial ratio a:b:c is toluene at 23"C, and employing a temperature cor- 0.82550:I :0.5851I . A powderpattern complete to 50o rection, is 2.79 g/cm3, in excellentagreement wih the N and obtained with a diffractometer and internal calculatedvalue of 2.80 g/cm3. Although most of the standard as indicated above is given in Table. 2. material is much too fractured and cloudy for gem Indexing of the reflectionswas accomplishedwith the applications, some clear sections, fully transparent assistanceof the single-crystalphotographs. and colorless,might be cut as gemstones.Zektzerite Relationshipsto other minerals fluorescesa light yellow color in short-waveultravio- let radiation. There is no responseto long-wave ul- Tuhualite, 4[(Na,K)rFez2+Fe|+Si,zOro.HrO], is or- traviolet radiation, and no phosphorescencein either thorhomic, Cmca,with a : 14.3I, b : 17.28,and c : wavelength. l0.l lA (Merlino, 1969).The near identity to the unit Zektzeite is almost isotropic, birefringence being cell and space group of zektzerite is obvious, and if 0.002. The mineral is biaxial negative with 2V" : the water in tuhualite is ignored, the atomic propor- -0'. The refractiveindices for sodium light are o : tions in the two minerals are also the same. Such 1.582,0: 1.584,and 7 : 1.584,all t 0.003,the optical orientation being X : a, Y : b, and Z : c. Table l. Chemical analysis of zektzerite The dispersionof the optic axesis very weak, r ) u. Nmber of Atoms LiNaZrSi6015 Zektzerite Atonic on the Basis Chemical composition Theoretical Analysls Proportions of 15 oxygens The idealizedformula of zektzeriteis LiNaZrSi.O,u Li.20 0.99 (Z : 8), with minor titanium and hafnium sub- Na20 1.01 stituting for zirconium. The mineral was chemically ZrO2 analyzed with an ARL-SEMQ electron microprobe using an operating voltage of l5kV and a sample Hf02 1.00 current of 0. l5 microamps. The intensitieswere cor- TrO2 rected by computer using Bence-Albeefactors.