352 



NATURE 



[November io, 192 i 



The Structure of Adularia and Moonstone. 

 By Dr. A. E. H. Tutton, F.R.S. 



A NEW and very promising scientific journal — 

 ■'*• Science Reports of the T6hoku Imperial Uni- 

 versity, Sendai, Japan, vol i, No. i — printed in 

 English at Tokio, has recently been issued (June, 

 192 1). It contains the results of an investigation, 

 commenced at Cambridge, by Mr. S. Kozu, who was 



Fig. 



-Adularia from St. Gotthard, plate 

 parallel (ooi). 



Fig. 2. — Moonstone from Ceylon, plate 

 parallel (ooi). 



assisted later in Japan by Y. Endo and M. Suzuki, on 

 the X-ray analysis of adularia felspar from the St. 

 Gotthard and the moonstone of Ceylon and Korea, 

 and on the influence of temperature on their atomic 

 arrangements. Adularia and moonstone are supposed 

 by mineralogists to be solid solutions of varying pro- 



of the monoclinic felspars by Mr. Kozu, the results 

 of which were communicated to the Mineralogic:;! 

 Society in 1916, showed that these constants are much 

 higher for moonstone than for adularia. This is due 

 to different molecular structure corresponding to a 

 different chemical composition, the optical constants 

 always increasing with the pre- 

 sence of soda, of which moon- 

 stone contains nearly three times 

 as much as adularia. 



When the cr\stals were sub- 

 mitted to X-ray analysis by the 

 Laue radiographic method, and 

 the radiograms compared, very 

 remarkable difterences were ob- 

 served. , In the case of adularia 

 all the spots were arranged on 

 single circles of the stereographic 

 projection of the radiogram, or, 

 in the case of the actual photo- 

 grapii, on ellipses, passing through 

 the centre of the figure, while 

 those of moonstone were in double 

 circles, as will be clear from the 

 two reproductions of the photo- 

 graphs themselves in Figs, i and 

 2, and of their stereographic pro- 

 jections in Figs. 3 and 4, 

 This indicates that adularia consists of a single kind 

 of space-lattice and forms a homogeneous solid solu- 

 tion, while moonstone consists of two kinds of space- 

 lattice, the atoms being distributed in two different 

 arrangements. The two components of moonstone 

 are not, however, pure potash felspar and pure soda 



• • • . 



Fig. 3. — Stereographic project! jn of Laue spots of adularia (ooi). 



portions of orthoclase (monoclinic potash felspar, 

 KAlSijO,), albite (triclinic soda felspar, NaAlSijOJ, 

 and anorthite (triclinic lime felspar, CaALSijOg), the 

 moonstone of Ceylon being regarded as a variety of 

 adularia exhibiting the property known as " schilleri- 

 zation," the exhibition of a pearly, sub-metallic, or 

 bronze-like lustre. But determinations made in Cam- 

 bridge of the refractive indices and optic axial angles 



NO. 2715, VOL. 108] 



Fig. 4. — Stereographic projection of I.aue spots of moonstone (ooi). 



felspar, but two kinds of solid solutions, both having 

 monoclinic symmetry. 



On heating the crystals a most interesting thing 

 happens. Nothing occurs up to 500° C, but then the 

 circles of spots corresponding to the structure richer 

 in soda begin to decrease in intensity and also con- 

 tinuously approach in position those of the arrange- 

 ment richer in potash, until at about 1060° C. the 



