620 Journal of Applied Microscopy. 



Joly. On the Change in Volume of Minerals Author calculates and records the co- 

 near their Fusion Point. Trans. R. Dubl. rr • ^ £ • r j- j 

 Soc. 6: 281 1807. efficient of expansion 01 diamond, 



augite and orthoclase at very high 



temperatures. The method is to photograph the sphere of the mineral at the 



different temperatures, these photographs being then very much enlarged and 



therefrom the coefficient of expansion calculated. 



INDIVIDUAL SPECIES. 



Calcite, with organic coloring matter. J. The calcite examined was translucent, 

 Fromme. Jahresber. ver. Naturwiss. Braun- chestnut-brown in color and occurred 

 schweig. 10: 104, 1897. . .u j uu • ^i tt . 



in weathered gabbro in the Hartz. 



Iron and manganese were absent. Coloring due to 0.2310 per cent, apocrenic 

 acid and 0.0135 per cent, of another organic acid, which must exist in combina- 

 tion as the calcium salts. Carbonated rain water takes up ammonia and humic 

 acids from the soil, and acting on the lime-feldspars of the gabbro would produce 

 the colored calcites. 



Calomel. Sur les proprietes optiques du Strong double refraction established by 

 H. Dufet. Bull. Soc. Min. 21 : 90, 1898. ^ . ■' 



measurements made on convenient 



artificial crystals. n£= 2.6559, noo =1.97325. (ne— nm) = 0.68268 (Na light). 



Dispersion very great, especially for the extraordinary ray. In convergent light 



the rings of the interference figure appear a little broken, but probably not on 



account of optical anomalies. l. mci. l. 



Mica Group, The Crystal Symmetry of the Author comments on very general ten- 

 Minerals of the. T.L.Walker. Am. Jour. ^^^ ^^ degradation from higher to 

 Sci., iv., 7: 199, 1899. J s . 1 , 



lower symmetry, shown by physical and 



morphological examination of minerals. Phlogopite and biotile^ in very thin 

 plates, proved to be triclinic and not monoclinic by marked divergence of axial 

 plane from parallelism with ray of percussion figure, and by asymmetric etch 

 figures of Wiik on basal cleavages. Thicker basal plates do not show this 

 divergence, probably due to polysynthetic twinning, with (001) as composition 

 face. Lithia micas appear monoclinic optically, but still show triclinic etched 

 figures (by Baumhauer and Wiik). Muscovite shown to be monoclinic optically 

 and by etched figures (by Leydolt, Baumhauer, and Wiik). Paper emphasizes 

 the conclusions of Wiik. l. McI. l. 



Periclase. Production artificielle de la, par un Caustic potash melted with magnesia 

 nouveau procede. A. de Schulten. Bull. ^^ ^ ^^\^^^ capsule tO a red heat, COoled 

 Soc. Min. 21 : 87, 1898. ^ , . . , , , . 



slowly, and after washing with chlorine 



water, crystals obtained and subsequently purified. Analysis shows 99.92 MgO, 



with trace of Fe. G. = 3.568 at 15°C. l. McI.l. 



Powellite Crystals from Michigan. C. Palache. -p^^ crystals ( J^ to 1 cm. in height) ob- 

 Am. Jour. Sci., iv, 7: 367,1899. , ,, • , 



tamed, pale bluish-green m color, 



translucent and with subadamantine lustre. G.=4.353 — 8. Measurements 



made on two-circle goniometer (Goldschmidt model) and angles recorded in 



cp and p. 



