STEVENSITE,REDBFINED AS A MEX4BEROF THE MONTX,IORILLONITEGROUP* GBoncB T. F.qusr aul K. J. Mun,tr.r., U. S- GeologicalSurtey, Washington,D. C. ABsrRAcr stevensite, a hydrous magnesium silicate, typically pseudomorphous after pectolite in basalt, has been restudied. X-ray difiraction analysis, staining tests, and differential ther- mal analysis all indicate that the mineral is a member of the montmrrillonite group of clay minerals. Stevensite difters from saponite in lacking essentiai amounts of aluminum and from hectorite in lacking lithium and fluorine. As is indicated by its formula, [Mgz eaMn.oz Fe.ullSir]oroloHlzx rs, stevensite has an abnormally low base-exchange capacity com- pared with the average value for montmorillonite of 0 37 equivalent per formula weight. This low capacity is believed to be due to the unique and probably restricted manner in which the charge deficiency apparently originates in the mineral-namely, through a deficiency in the total numb:r of ions in positions of octahedral coordination. Multivalent ions, whose higher charge rvould compensate for the deficiency in number, as in sauconite, are practically absent in stevensite. Hrsronv oF STEVENSTTE AND Irs Svxorqvus ProfessorAlbert R. Leeds, of the Stevens Institute of Technology, Hoboken, New Jersey, in 1873 published a description and analysis of a mineral which he calied talc pseudomorphousafter pectolite. An exami- nation of his paper (Leeds,1873) shows,however, that he was not con- vinced of the interpretation of his analysis,for he writes (p' 24): ,,While closely approaching talc in its physical properties this pseudomorph after pectolite is near sepiolite in its chemical composition." The mineral which he analyzed was found "in veins of calcite which traverse the trap rock in the vicinity of Bergen Hiil Tunnel, Hoboken, New Jersey."His analysis,Table 1, showsthat his samplewas nearly but not quite pure. According to Chester (1896) the name stevensitewas subsequently proposed.by Leedsin 1873in honor of E. A. Stevens,the founder of the StevensInstitute of Technology.Chester (p. 257) describesthe naming as follows: "This name was suggestedin 1873at a meeting of the N' Y' Lyceum of Natural History, but not published though soon after used on labels." Chestercites a referenceto a note by Leeds published in "The Naturalists Leisure Hour" for 1889, but a search of two copies of this publication (from the Library of congress and the American Museum of * Publication authorized by the Director, U. S' Geological Survey' 973 GEORGET. FAUST AND K. J. MURATA 6 o a ! 'dnb0i +1 q.+N4O,ca O.,\O o r N EiHN@O j | \ON i o .ts; I l*'+t b2 az *€r'dc;*c; a a v a Fr ts OOOONOOHO +' x 54- aOOOOiONOO o\ -i cioJc;ddoi c;.i I Pz. 40 |J H E z o N*1 c)4co N r O re\OQAN I . .* '@ ,i| ,EaO\OOn| I i8 N z E.v tsl N N \ONaiO ts N \o I rNrooNn O | | . .* | ,E'EX \o o , | 4<1 \oo4 A5X 6TE qN .:H a oSl A i 6= .+ cO cOiO\O\ \O € - r*co44 rN AO | . | .+ | F >o t2 o i I oo\N4 r\o (n d^ hN 6+ q/B a etrr t4 a FJ |.l o N o\oi€ b riil ooro\o\oN'<r z | . 't .* | € O 'ON-O r@ NN d a O : o € O 4N N4\Oi O -i9P^ 4O lN\O4<f,l | | O r HN oH,oo€i| | a .ao \ON r.1 a a F O .9. <o\ O oN oiNNOSNO\ o 'ii- O Zt> dO trN<rO\OO*\O d .22 6i ;€o ic;\cjod- 6€ a a v E z F d a cd s?EcEBsEsss" z Fl STEVENSITE KEDEFINED 975 Natural History) failed to reveal any mention of the naming of this mineral. Chester also cites the erroneoususage of stevenite for stevensite. After Leeds' work was published two other closely related magnesium silicates were described.Heddle (1880) named a magnesium silicate from Corstorphine Hill, Scotland, walkerite. Walkerite (not walkererde of Hintze:walkerite of Dana's Systemof Mineralogy,1892) contains5.12 per cent MgO. (SeeTable 1.) Reuning (1907)described a mineral which he called magnesiumpektolith (magnesium pectolite) from the diabase at Burg bei Herborn, Driesdorf, Germany. Valiant (t904) included stevensite in his list of New Jersey mineral Iocalities. The problem of the character and composition of stevensite was re- opened by Glenn (1916). He made an analysis of stevensiteand of a partly altered specimen of pectolite from the Hartshorn quarry in Springfield Township, Essex County, New Jersey.From a study of these two analyseshe concluded that walkerite and magnesiumpektolith were mixtures of stevensite and pectolite. Hilgard (1916) found a peculiar clay at Hacienda Santa Lucia near Mexico City which on analysisshowed 17.10per cent MgO. He named this mineral lucianite. Rogers (1917) in a review of the status of amorphous minerals sug- gested that (1) "stevensite . is probably the amorphous equivalent of crystalline talc" and (2), referring to lucianite, Hilgard's clay, "This substance. is probably a synonym of stevensite." The occurrenceof stevensite at nine localities in the Watchung basalt of New Jerseyis given by Manchester(1931), who consideredit to be a variety of talc. Lorent (1933)in studying the hydrothermal alteration of thelimburg- ite of Sasbachin the Kaiserstuhl discovered a gel-like substance which he called a "magnesiumsilikatgel." Analysis of a sample weighing only 0.3793 gram showedit to consist of 46.1 per cent HzO;26.7 SiO2,2.8 AlzOs,0.6CaO and24.7 MgO; sum:99.7 pet cent. The ratio of MgO to SiOr showsthat this mineral, if homogeneous,is not stevensite. Stevensitewas reported in the matrix of the Mayville iron ore of Wis- consin by Hawley and Beavan (1934), who identified it by optical and microchemical tests. Selfridge (1936) included some data on stevensite in his paper on the serpentine minerals. He listed stevensite with deweylite and commented as follows (p. a8a): "No explanationcould be found for the higher indices of No.51. Duplicate x-ray patterns show that it is deweylite'Optically it approachesserpentine," and (on p. 500) "The deweylite pattern of SpecimenNo. 51, which displayed optical characterssimilar to those near 976 GEORGET. FAUST AND R. J. MARATA the low index of serpentine,indicates the need for further study between deweylite and serpentine.', The most detailed description of stevensite appeared in the Ergiin- zungsbandof Hintze's Handbuch der Mineralogie (1936-1937),where two pages (649-650) are devoted to the description of this mineral and its synonymy. strunz (1941) in his Mineralogische Tabellen consideredstevensite to be talc pseudomorphousafter pectolite; walkerite to be weathered pecto- lite; and Iucianite to be stevensite(amorphous talc?). Ross and Hendricks (1945) in their paper on the minerals of the mont- morillonite group observed that the lucianite of Hilgard is "essentially similar to saponite and difiers only in being a little higher in calcium oxide and lower in magnesiathan most saponites.', Hey (1950) in his book, An index of mineral speciesand varieties, lists stevensite as "talc pseudomorphousafter pectolite"; walkerite as a variety of pectolite, and gives as a synonym magnesium-pectolite. He also interprets lucianite as "probably an impure saponite." Dnscnrprroxs or, THE SpBcruBNsSruorrn StevensiteNo. 1. Locality: Springfield,New Jersey (U.S.N.M. R4719). Pseudomorphousafter pectolite. Pink masses.Analysis 1, Table 1. SteaensiteNo. 2. Locality: Jersey City, New Jersey (SelfridgeNo.51). Deweylite, "Serpentine after pectolite.,' Amber masses.Analysis 9, Table 1. SteaensiteNo. 3. Locality: Paterson,New Jersey(F-1104) . pseudomor- phous after pectolite. Buff, in part resinous in appearance. Pectol.iteNo. 1.Locality: Paterson,New Jersey(F-1103). White, radiating needles. X-ney PowoBn DrtlnacrroN Sruoy X-ray powder diffraction patterns of stevensite, saponite, and pecto- Iite, made from spindles prepared with Duco cement or celluloseacerate dissolved in toluene as the binder, were obtained using filtered copper radiation. rndices were assignedto stevensite on the basis of the work of Faust (1951) on the related mineral sauconite. The data in Table 2 show that the r-ray powder diffraction data for stevensite are practically identical with those of the montmorillonite mineral saponite. The measurementsin Table 2 weremade on stevensiteNo. 1 dried at room temperature. A small amount of stevensite was treated with ethyl- eneglycol, and it was found that (001) advancedfrom 14+ A to 15.1A. STEVENSITE REDEFINED 977 StevensiteNo. 3, from Paterson,New Jersey,yielded a pattern showing (001),-forair-dried material mounted in ethyl cellulosein toluene,to be 16+A. Tl'rl-n 2. X-nlv Powlun Dara ron SrEvnnsrrn, Saeowrrn, aun Talc Dnrno a.r Roolr TBupnnarunr (CulNi; I:1.5418 A) Stevensite No. 1 Saponite, Cathkin near Springfield, New Jersey Glasgow, Scotland U S.N,M. R4719 Miller d(A) Miller d(A) Notes d(kx) Indices Indices (001) 14.t Showsa (000 14.8 (002) 7.7r m Broad 9.4 5. 14 Center of (003) s 14 m Broad Duco band 4.69 (110)(020) 4.ss (110)(020) 4.se ms Broad +.34 wf (004) 3.7e 3.88 1b (oos)? 3.20 m (00s) 3.09 m 337 3 3_11 10 (130) 2.63 -l 2.613 270 1 I Not a good 2.59 2 (200) 2.53 w-m.J separatron (2oo) 2.s4s m ulnusc 2.47 5 (220)(040) 2.284 w Difiuse wf 2.20 2.O9 (240) !.722 (1s0) | 747 1.92 (310) 1.703 1.86 (060) l.5lo (060) 1.543 s Broad | 725 1.498 wvf r.67 1.458 vwf 1 652 (260)(170) 1 3r5 mw r 327 m Broad 1.632 b (400) | 265 1.278 wvf Broad l. )J 0.999 vwf Diffuse 1.52 (290)(460) 0 eeo 1.501 (380)(s20) 1 461 (480) 0.879 (sso)(3e0) 0.8e0 wvf Broad 1.446 1.405 1.390 3b 1.330 2 1.315 2 t.291 2 Stevensite No.