A description is given of structural imperfections such as twinning, lineage sutures and optical streaks, in Alpine quartz crystal

Friedlaender, C.

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Structural Imperfections in Alpine Quartz Crystals 217Structural Imperfections in Alpine Quartz Crystals(PLATE VII)By C. FRIEDLAENDERABSTRACTA description is given of structural imperfections such as twinning,lineage sutures and optical streaks, in Alpine quartz crystals.AT the suggestion of Professor Niggli, the " usability " of Alpine- quartz crystals for piezoelectric communication equipment wassystematically investigated. It was ascertained that carefully selectedparts of Alpine quartz crystals gave quite satisfactory results (Fried-laender, 1944, 1951 ; Friedlaender and Locher, 1945 ; Hedinger,1948). The inadequate total quantity of available high-grade Alpinequartz crystals sets rather narrow limits to their use. Furthermore,a precision orientation may be rendered deceptive by characteristicstructural imperfections. Whereas the technical importance of Alpinequartz is slight, at least in normal times, some of the observations mademay be of general interest.Twinning.—Dauphine twinning was found to some extent in allAlpine quartz crystals examined. With respect to the extent of twinningand to the course of the twin boundaries within the crystal, differenttypes can be distinguished ranging from almost complete absence ofDauphine twinning to intricate twinning throughout the whole crystal.Generally speaking, the twin boundaries grow more intricate towardthe apex of the crystal, that is to say with decreasing temperature,while the bottom of the crystals frequently show a far simpler patternof intergrowth of the parts of a Dauphine twin. There is obviouslya fundamental difference between Dauphine and Brazil twinning.R-L twins appear, in fact, not to be developed with the same facilityas Dauphine twins where both parts involved are of the same hand.From morphological evidence only, Brazil twinning is recognizablein Alpine quartz crystals in very rare instances. It is fairly frequent,however, in small peripheral regions of evidently late formation relativeto the host crystal, as satellite crystals in the sense of Gaudefroy (1933).Lineage Sutures.—According to a commonly held belief, Alpinequartz crystals could not be used at all for piezoelectric applicationson account of their intricate twinning. This belief very likely wasfounded on an erroneous interpretation of the sutures : they arefrequently taken as an indication of twinning. The sutures, seam-likelines running roughly parallel the c-axis, cut the horizontal striationon prism faces which is due to alternation of prism- and steep rhombo-hedral planes so as to cause a marked discontinuity. While thereVOL. LXXXIX—NO. 3 18https://doi.org/10.1017/S0016756800067625Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:14:05, subject to the218 C. Friedlaender—•are true twinning seams, it must be emphasized that these sutures arequite distinct from twinning. On the other hand, the sutures are anindication of lineage structure such as occurs frequently and in manyminerals (see Buerger, 1934). A line drawing (Text-fig. 1) schematicallyshows the internal lineage and twin structure of an Alpine quartzcrystal; the sutures are seen to be independent of the twin boundaries.TEXT-FIG. 1.—Schematic diagram of an Alpine quartz crystal of hexagonalhabit. The crystal is dissected by four cuts normal to the c-axisinto five parts. The rhombohedral faces show natural etching,sutures, and horizontal striation.Z-slab 1 : on polished Z-plane, lamellar lineage boundaries(represented with some exaggeration). Sutures on prism facesintersected by horizontal striation.Z-slab 2 : etched Z-plane shows intricate boundaries of Dauphinetwinning and small region with Brazil twinning. Prism facing frontfinely gound and etched so as to show course of twin boundaries.•> Z-slab 3 : Z-plane and one prism face etched.id. on Z-cut of basal portion of the crystal. Twin boundariesare seen to be far simpler in basal part of crystal than in upperpart.Throughout, lineage sutures independent of twinning.Optical Streaks.—Viewed in parallel light, a slab of a certain thick-ness and with two polished parallel faces (as represented in the Z-slab 1of Text-fig. 1) will reveal optical streaks, similar to those observedwhen dissolving sugar in water. These streaks (Plate VII, fig. 1),however, are not due to dissolution of any foreign material ; theyare accounted for solely by a slight difference in orientation of adjoininglamellae. If the optical axes of adjoining lamellae in a quartz crystaldiffer from each other, there will be a certain difference in refraction,ny — Hyi. For a difference in orientation of 3°, nyl would be 1 -5534x cos 3° = 1-5508 ; ny - nyl = 0-0026. For a difference of 4Dbetween adjoining lamellae, n.y\ would be 1-5492 and ny — nyihttps://doi.org/10.1017/S0016756800067625Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:14:05, subject to theStructural Imperfections in Alpine Quartz Crystals 2190-0042. Differences of refraction of that importance must be quiteperceptible.In a thick slab, there will be a considerable amount of superposition.This may explain the observation that the streaks seem to lie nearerto each other than would be inferred from observation in any planenormal to the viewing direction and that on tilting the slab slightlythe streaks appear to move. In polarized light, polished Z-slabsreveal contrasting patches of strong interference colours. This is dueto the optical activity and to the lineage structure.Some observations of optical streaks in polished quartz slabs havebeen described by various authors (Kundt, 1883 ; Laemmlein, 1937 ;Topler, 1864, 1866, 1867 ; Weil, 1931), but no explanation had beenattempted. The observation of streaks in polished slabs presentsa very sensitive means of detecting structural imperfections.The lineage structure is clearly recognized when plates cut parallel tothe c-axis, as X-cuts and Y-cuts, are viewed in polarized light. Asa rule such a plate prepared from an Alpine crystal will not extinguishuniformly. One may observe differences in the orientation of the c-axtsof adjoining lineages up to 3°. Laue diagrams within single lineagesappear normal apart from showing a rotation of about 3° around thec-axis ; the superposition of lineages results in doubling of X-rayspots.On observation with low power magnification, the borders andtermination of the lineages become discernible as irregularly tilted,wedge-like seams of birefringence (Plate VII, fig. 2). A very conspicuousdeviation of the lineages may be reminiscent of accessory heteroaxialtwinning (Plate VII, fig. 3).REFERENCESBUERGER, M. J., 1934. The lineage structure of crystals. Zeit. Krist., lxxxix,195-220.FRIEDLAENDER, C, 1944. Untersuchungen an alpinen Quarzen. Verhandl.Schweiz- Naturf. Ges., cxxiv, p. 119.1951. Untersuchungen iiber die Eignung alpiner Quarze fur piezo-elektrische Zwecke. Geol. Schweiz., Geotechn. Ser., xxix, Berne.and LOCHER, F., 1945. Vorlaiifige Untersuchungsergebnisse iiber dieEignung alpiner Quarze fur piezoelektrische Zwecke. Viertel-iahrsschr. Naturf. Ges. Zurich, xc, 126-135.GAUDEFROY, C, 1933. Sur les groupements de cristaux de quartz a axesparalleles. Bull. Soc. Franc. Min., Ivi, 5-63.HEDINGER, R., 1948. Untersuchungen iiber das piezoelektrische Verhaltenalpinen Bergkristalle. Promotionsarbeit E.T.H., Zurich ; Schmid-berger and Miiller, Kilchberg (Zurich).KUNDT, A., 1883. Benutzung der Schlierenmethode zur Untersuchung vonVerwachsungen im Quarz. Ann. Physik und Chemie, N.F., xx,688-690.LAEMMLEIN, G. G., 1937. Observations on the twisted quartz. Bull. Acad.Sci. URSS. CI. Mat. Sci., 937-964.TOPLER, A., 1864. Beobachtungen nach einer neuen optischen Methode.Max Cohen and Co., Bonn.https://doi.org/10.1017/S0016756800067625Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:14:05, subject to the220 Structural Imperfections in Alpine Quartz CrystalsTOPLER, A., 1866. Ueber die Methode der Schlierenbeobachtung als mikro-skopisches Hilfsmittel, etc., Pogg. Ann., cxxvii, 556-580.1867. Optische Studien nach der Methode der Schlierenbeobachtung.Pogg. Ann., cxxxi, 33-5.WEIL, R., 1931. Quelques observations concernant la structure du quartz.C.R.l'e Reunion Inst. Optique, p. 11.CARMENSTRASSE 45,ZURICH 32,SWITZERLAND.EXPLANATION OF PLATE VIIFIGURE 1.—Optical streaks. Polished Z-slab, about 2 cm. thick, of R-quartz,Furka. Length of crystal 25-7 cm., diameter 8 cm. Viewed inparallel light, 1:1.FIGURE 2.—Lineage structure. Borders and termination of lamellae, X-cutplate, 1 mm. thick, Z running N.-S. L-quartz, Goscheneralp.Seams of birefringence, reveal tilting and divergence in orientationof adjoining lamellae. Polarized light. 18 : 1.FIGURE 3.—Lineage structure. Borders of lamellae. X-cut plate, 1 mm.thick, Z running N.-S., L-quartz, Goscheneralp. Seams of bire-fringence reveal divergence of orientation suggesting analogy tohetero-axial twin. Polarized light. 18 : 1.ANNOUNCEMENTEMPIRE MINING AND METALLURGICAL CONGRESSThe Fifth Empire Mining and Metallurgical Congress will beheld in Australia during April and May, 1953, at the invitation of theCommonwealth of Australia and the Dominion of New Zealand.Full details are given in the First Circular, which can be obtained from :The Secretary,Fifth Empire Mining and Metallurgical Congress,399 Little Collins Street,Melbourne,Victoria, Australia.https://doi.org/10.1017/S0016756800067625Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:14:05, subject to theGEOL. MAG. 1952. PLATE VII.FIG. 1.FIG. 2. FIG. 3.STRUCTURAL IMPERFECTIONS IN ALPINE QUARTZ.https://doi.org/10.1017/S0016756800067625Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:14:05, subject to the

Structural Imperfections in Alpine Quartz Crystals

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