CRESTMORE SKY BLUE MARBLE, ITS LINEAR THERMAL EXPANSION AND COLOR

Transcription

1 CRESTMORE SKY BLE MARBLE, ITS LINEAR THERMAL EXPANSION AND COLOR Jsnen L. RsBxnlz AND Duny T. Sun, Rensselae Pl^'ttechnic Institute. Tt. Nezp Yk. Aslc Themal studies wee made f the Sky Blue mable fm Cestme, Califnia. The cefficients f linea themal expansin wee detemined fm 20 t 700' C. f specimens cut with N-S, B-W and vetical gegaphic ientatins. Fist cycle values ae vey high and indicate a cnditin f high stain which is lagely elieved by heat teatment. The cmputed ptic axis cncentatin shws a maked E-W pefeed ientatin which may be celated with the gelgical stuctue. The sky-blue cl is attibuted t esidual stain. INnucN Themal studies f iented specimens f Yule mable (1) have lndicated the pssibility f cejating linea themal expansin with the stesses invlved in defmatinal pcesses. D. Eleana B. Knpf, in discussing this questin with Pfess A. O. Wdfd f Pmna Cllege, suggested that such an investigatin f the Sky Blue mable fund at Cestme might pesent inteesting esults. Thugh the kindness f Pfess Wdfd, seveal lage samples wee cllected in the field, sme f which wee iented as t dip and stike. The gain size is s vaied that thee was hpe f btaining a few sufficiently lage gains t withstand the igs f cutting iented specimens and theeby pemit single cystal studies t be made. nftunately, nne culd be btained lage enugh f this pupse and, thugh Pfess Wdfd's effts, suitable specimens wee selected having a )-3 mm. gain size. Test sepcimens wee cut fm a single field sample taken fm the Cmmecial Quay, Cestme, Califnia, at abut 900' elevatin, 2700' East and 1500' Nth, Riveside Cement Cmpany cdinates. The field sample suface dipped 27" E. and the stike was N 10 E. Test specimens having N-S, E-W., and vetical ientatins wee cut fm this sample. Pncpunn The methd used f measuement f the cefficient f linea themal expansin, a, has been fully descibed (1). In de t detemine the effect f heat teatment upn the elief f pemanent stain, the tw cycle heating-cling technique was fllwed. Expeience with Yule mable indicated the pssibility f intducing what appea t be themal stains in the vicinity f 350. In an attempt t eliminate this pssibility, 1049

2 1050 J. L. ROSENHOLTZ AND D. T. SMITH a seies f iented specimens wee fist studied cyclically t 400 C. The length ecvey afte the secnd heating cycle was much geate than it shuld have been had the defmatinal stains been emved. It was theefe decided t pceed exactly as in the case f the Yule mable and t use tw heating-clipg cycles t 7000 C. The values f the cefficients f themal expansin ae given in Table 1 f each gegaphic ientatin and f bth heatihg-cling cycles' T.tsln 1. CcnNs LNn.c'n TnnnM'q.L Expelsx Cnnsn Sxv B,u Mens Fist Heating-Cling CYcle 20" C. t N-SX106 "-*"tu VeticalX 106 Vlume cefficient X 106 calc. 100" 200" 300' ' 600' 700" 6.M ' t. JJ t J+.+J Ol Length ecvey afte cling s Secnd Heating-Cling Cycle 20' C. t N-SX106 E-WX106 VeticalX 106 Vlume cefficient X106 calc. 100" 200" 300' " 600' 700' R (C Length ecvey afte cling 0.tT 0, The cuves shwn in Fig. 1 indicate that the ate f incease f a is me egula afte the stains ae elieved duing the fist heating-cling cycle. F cmpaisn with a calcite single cystal, the calculated vlume

3 LINEAR THERMAL EXPANSION OF CRESTMORE BLE MARBLE ?n, 25 6z a z c x u 15 F zu l tl s l TEMPERATRE IN DEGREES C. Fc. 1. The cefficients f linea themal expansin fm 20 C. f tw heatingcling cycles f Cestme Sky Blue mable. expansin cefficients ae shwn in Fig. 2. The cespndence at 100 is vey gd between calcite and secnd cycle mable. This is an indicatin that stuctual stains have been lagely emved. As the tempeatue is inceased, hweve, the vlume change in the mable diveges appeciably. This may well be due t the intductin f stains induced by heating because f the maked anistpy f themal expansin f calcite. OnBxaN l E MansB Wdfd (2) has fund that, while the stuctue at Cestme is quite uncetain, thee ae sme bsevable suggestins f bedding having an

4 052 J. L. ROSENHOLTZ AND D. T. SMITH eastely dip. He indicates* that, f the aea fm which the field specimen was btained, any expansive fce elated t the intusin f the quatz mnznite pphyy wuld pbably have been diected appximately in the same diectin as the nmal t the pblematical bedding planes in the mable. This indicates a maximum stess in the E-W diectin whethe themal defmatinal stesses bth ae invlved. 80 z. a z _- 50 f, d40 z. 3Q td,"': JL 320 cat9e t."u*x*.1i.n*l? F. 2. Calculated cefficients f vlume themal expansin fm 20 C. f Cestme Sky Blue mable and a calcite single cystal. The auths have ecently made studies f linea themal expansin f cmpessed cylindes f magnesium and medium sft steel (3). They fund that a inceases in a stess ange beginning at the yield pint and cntinuing until extensive plastic defmatin ccus, afte which it begins t decease. It is infeed, theefe, that a high value f a may be celated with a lage stess histy and, since a f Sky Blue mable is a maximum in the E-W ientatin, it is lgical t assume that this was the diectin f maximum stess. Althugh the stuctual details * Pesnal cmmunicatin.

5 LINEARTHERMALEXPANSI1NFCRESTM)REBLEMAfuBLE1053 ae nt clea, this assumptin cespnds with the available field facts and may be used t pint the way in the evaluatin f bscue field infmatin. As f pefeed gain ientatin, calculatins based upn the ceff.cients btained fm the secnd heating-cling cycle at c. indicate that 59 pe cent f the gains have thei ptic axes cncentated in the E-W diectin, with 25 pe cent N-S and 16 pe cent vetical. Althugh these calculated cncentatins ae based upn the assumptin that nly c ientatins exist in each gegaphic diectin, the esults shw the decided pefeence in the E-W diectin. TnB C-n l Sv B-uB MenaB The name f this ecystallized limestne is mst desciptive f its cl. Of paticula inteest is the fact that the blue mable makes an iegula eivelpe 100 t 150 feet thick, abut an intusin l quatz mnznite pphyy; it is, in tun, envelped by white mable' The blue mable, which appeas quite unifm t the unaided eye, shws micscpic black segegatins scatteed thughut. Segegatins which have been weatheed slightly ae suunded by feic xide stains. Small pieces f the blue mable wee heated t vaius tempeatues, beginning at 1000 C. and inceasing by 25 intevals. The samples wee held at each tempeatue f 30 minutes. The fist bsevable fading was pduced by heating at2250 C; it was me pnunced at 2500 and was cmplete at 275", e\ulting in a light ceam-white cl. If the heating ate is nt sufficiently slw, the blue mable samples shatte explsively int white cleavage fagments in the vicinity l 275 C. It seemed advisable t ascetain whethe the cl changes nted might be d.ue t chemical efiects. Pfess Athu A. Bu f Rensselae Plytechnic fnstitute kindly ageed t make spectgaphic and pwde -ay examinatins f the blue mable as well as specimens which wee heated t 275" and 700 C., in de t seek ut pssible cling cnstituents. The spectgaphic examinatin shwed a small amunt f in and n the cling elementsl futheme, the cncentatin f in was the same in all thee specimens. N iegulaities f any kind wee evealed by the -ay examinatin. While stuctual stain is eadily shwn by x-ay, in this case the stain was dubtless elieved by the pulveizatin. It is bvius that the cl change induced by heat teatment unde 3000 c. was nt due t chemical changes. The nly appaent easn f the blue cl appeas t be esidual stain which is elieved by heating. It ls pefectly easnable t assume that stuctual changes due t themal defmatinal stesses may pduce pnunced cl effects.

6 1054 J. L. ROSENEOLTZ AND D. T. SMITH This cnditin may be bught abut in sme allys by cld wking pcesses and it may well be that paticula stess cnditins can pduce cl changes in calcite. This aises the lage questin as t why mst mables ae nt blue. Disegading definite cling cnstituents, stess cnditins ae s vaiable, bth as t chaacte and intensity, that the answe cannt be knwn until the specific cnditins which ae cl inducing ae discveed. Acxw,nGMENTS This eseach was made pssible by assistance fm the Rensselae Plytechnic nstitute Reseach Fund. The auths ae especiallv sateful t Pfess Wdfd f cllecting the specimens u.i f. itj-utin he has supplied elative t field bsevatins. They als ae indebted t Pfess Bu f hig spectgaphic and.-ay examinatins f the mable specimens. Rnennxcns 1. RseNnlz, J. L., ann Sun, D. T.: Am. Minel., J (lg4g) 2. Wn, A. O.: Calif. f u. Mines and Gelgy, ReptXXXD(, State Minealgist, July 1943, Rspxnlz,!.L., an Sunn, D.T.: J. Appt. Phys.,2l, (lg10).