NOTES AND NEWS 1307
RrrnnaNcss
Amxaxorn, G. B., HosroN, W. M., arn h,rn, H. K' (1954) The solubility of amorphous silica in water: -f. Phys. Chem.58,453-455. Cr-anrr', C. w (1924) The data of geochemistry : LI' S ' Geol' Suney BuIl' 77o' 841 p' CoNn.tr, T. A. (1346) Observations on the geology of East Floricla: Am. Jour' Sci',ser 2, 2, 36-48. CoorB, C. Wvrnr, aNo Mossou, Sruanr (1929) Geology of Florida: Florida State Geol Survey 20th annual rpt ,227 p. Kn.Lusrorn, KoNnm B. (1956) Dissolution and precipitation of silica at low tempera- tures'. Geockim. et Cosmochim Acta 10, l-26. Smvrn, RevuoNn (1957) The silica budget in the sedimentary cycle: Am. Minerol' 42, 821-841. Wnrrr, Donnrr E., Bna.NNocH,W. W., AND MuRArA, K J. (1956) Silica in hot spring waters: Geochim.et Cosmoclti'tn.AcLa lO,27-59.
THE AMERITAN MINERALOGIST. VOL 1.5,NOVEMBER DECEMBER, 1960
VOLBORTHITEFROM BRITISH COLUMBIA
J. L. Jeueox, Ot'tawa,Canada' Volborthite,Cue(VOa)z'3HzO, is presentas a weatheringproduct of a thin, interlava sedimentaryrock of Upper Triassic age which crops out west of \Ienzies Bay on Vancouver Island, and north of Gowland Har- bour on QuadraIsland, British Columbia. The vanadium-bearingrock is a black, extremelyfinely laminated,fos- siliferous,non-clastic sediment which consistschiefly of carbonaceous matter and microcrystallineto cryptocrystallinequartz. Spectrographic analysesindicate that the carbonaceousmaterial contains vanadium. Hypogene chalcociteis generallyan additional major constituent of the sediment,in somecases making up over 50/6 of the rock. The associated volcanic flows are predominantly pillowform and massive porphyritic basalts,andesites, and spilites which are commonly amygdaloidal.The amygdule material is largely qtartz, calcite, chlorite' zeolites,epidote, and pumpellyite. Prehnite, chalcocite,chalcopyrite, bornite, and native copper,as amygdule filiings, are widespreadin small amounts; analcite' heulandite,and greenockiteare of rare occurrence. Minor quantitiesof volborthite coat exposedsurfaces of the laminated sediment, but the mineral is more abundant along planes exposedby splitting the rock along the laminae.
Pnvsrc.qr PnoprntrBs The vanadate assumesmany colors and habits, most of which are briefly summarizedbelow: 1308 NOTESAND NEWS
Dark green to yellowish green, habit massive, compact, with good cleavage.Scaly crusts and rosette-like,honey-combed, or boxwork-like aggregates.Scales with a triangular or hexagonaloutiine, occasionally with impurities some distancefrom the center arrangedin a hexagonal outline. Scaly bright yellow to brownishyellow incrustationson massive or cleavableemerald green to dark greenhexagonal cores of up to 0.6 mm. diameter. Yellow, brownish yellow, light brown, and blackish brown, with habit flocculentorreticulated;also radiating fibrousand circular in outline, occurringsingly or in groups,usually with a successionof colored zonesand a minute, massive,central teat. Less commonly bright yellow and spherulitic. Most of the British Columbia volborthite is yellow or brownishyellow. The mineral is translucentin immersionoil, and not pleochroic.Lamellar twinning is common; the units are length fast and are twinned in a plane almost perpendicularto perfect (001) cleavage.Rare plaid twinning was also observed. The measured indices, determined on yellowish green scalesand cleavagefragments, depart greatly from thosereported in the literature:
a 1.793+ .005 Biaxial negative p 1.801+ .005 (-) 2Vlarge r 1.816+ .005 r Habit Minor Strong trace Flocculent Cu, V Si, AI Ca Flocculent Cu,V Ai si, ca Ilexagonal coresl cu,v Si Fe, Al Rosette scales Cu, V Si Al, Mg, Ca I Identical results were obtained from three seDarate analvses. Ca is present in trace amounts, X-ray powder photographsof volborthite were taken with 57.3 and 114.59mm. diameter Philips cameras,using nickel-filteredcopper radia- tion. The observed intensities and measured spacings (corrected for shrinkage)are listed in Table II. fhe British Columbia volborthite is associatedwith abundant mala- chite and brochantite, and small amounts of cuprite, tenorite, azurite, calcite,cyanotrichite, connellite, and an unidentified light blue hydrous copper sulphate. Although carnotite was reported from the locality by NOTES AND NEWS 1309 Tasln II. Vor,nonrnrrn; X-Rev Pomnn ParronN d(meas)A d(meas) A d(meas)A I 7.9 264 4 r.79 10 7.t8 6 2.57 A t.7r I /! 2 5.15 \2 2.46 1.68 I I 2 4.43 6 2.39 2 I.J/ I I I 2 4.26 2 2.28 2 1.55 4.10 n 2.23 5 1.51 I I J 2 3.59 2 2.13 1.50 1 3.r0 J 2.04 1.49 /L 4 3.00 \2 1.96 r.47 I 6 2.88 2 1.92 1.46 n 2.72 I .80 T:M t.43 Ellsworth (1932), no additional carnotite or uranium minerals have been found in the area.The maximum reportedvalue of VzOrin the sediment is over 3 per cent, but the lack of sufficientquantities of the copper and vanadium-bearingrock hasresulted in the depositsgenerally being classi- fied as uneconomical. AcrNowrnncMENT The writer is grateful for the supervisionand assistanceof Dr. R. M. Thompson,Professor of Mineralogy, the University of British Columbia. RrlBrurcn Er,r.swontn, H. V. (1932): Rare-element Minerals of Canada; Geol'. Suro., Canada, Economic Geol.Ser. ll, 139. THE AMERICAN MINERALOGIST, VOL. 45, NOVEMBER-DECENIBER, 1960 THE BULK COMPOSITIONOF A ZONED CRYSTAL" ANnnBw Gnrscou, U. S. GeologicalSurvey, Washington, D. C. Quantitative petrographic studies often require an estimate of the bulk compositionof zonedcrystals, such as plagioclasefeldspars. Bowen (1928,p. 143) pointed out in this connectionthat "the outer shell of a crystal requires to have only about one-tenth the thickness of the whole crystal in order to constitute half the volume." X-ray or oil immersion methods of bulk composition determination sufier from similar diffi- * Publication authorized by the Director, U. S. Geological Survey.