146 



CARNEGIE INSTITUTION OF WASHINGTON. 



(15) Das ternare System: Diopsid-For3terit-Silicium-2-oxyd. N. L. Bowen. Z. anorg. 



Chem., 90, 1-66 (1914). 

 A German translation of "The ternary system: diopside-forsterite-silica " 

 (Am. Jour. Sci. (4), 38, 207-264: 1914). Reviewed under No. 14 above. 



(16) The composition of rockallito. Henry S. Washington. Quart. J. Gcol. Soc, 70, 



294-302 (1914). 

 The paper is a chemical study of a unique agirite granite from the islet of 

 Rockall, north of Ireland. Only three small specimens are known, and that 

 examined was generously given through Professor J. W. Judd by the Governors 

 of the Imperial College of Science. A very complete chemical analysis was 

 made, which confirms in the general features one made some years ago in 

 England. It shows, in addition, the presence of large amounts of zirconia and 

 ceria — the amount of the latter being next to the highest yet known for igneous 

 rocks. By comparison with the minerals present in the rock, it is shown that 

 these two oxides belong to the pyroxenes, and the probability is pointed out that 

 the presence of these two oxides is characteristic of acmite as contrasted with 

 their absence in the closely related segirite. Further study of this point will 

 be undertaken when material from Norway, to be furnished through the kind- 

 ness of Professor Brogger, is received. 



(17) The crystallographic and optic properties of magnesium and manganese pyrophos- 



phates. Olaf Andersen. J. Wash. Acad. Sci., 4, 318-325 (1914). 



Pyrophosphates of magnesium and manganese were obtained in crystals by 

 cooling the melts of the pure substances. 



The magnesium pyrophosphate (Mg2P207) is monoclinic (axial ratios a :b:c = 

 0.7947 : 1 : 1.0880; /3 = 75° 49'), forming tabular crystals composed of numerous 

 small individuals in parallel intergrowth. Forms: c(OOl); 2(110); r(lOl); 

 a:(112). Colorless. Hardness about 4. Cleavage perfect after z and good 

 25\ 

 4/ 



microscope: 7jva= 1.615; |SA^a= 1.604; aAra= 1-602. Optical character positive. 

 Axial angle 2V =20|° (2E =33°). Optical orientation: Plane of optic axis 

 (010) 5.Ta = 7=a — axis. 



Manganese pyrophosphate is also monoclinic, with very nearly the same 

 crystallographic properties as the magnesium pyrophosphate (a:h:c = 

 0.7834: 1 : ?; /3 =74°90. The crystal habit is prismatic. Forms: c(OOl); 

 a(lOO); 2(110). Color brownish pink. Hardness about 5. Cleavage perfect 



along 2 and poor parallel to c. Density (? (^) =3.707. 



Optical properties: 7,va=1.710; |8jva = l-704; 0^^0 = 1.695. 



Optical character positive. Axial angle large, estimated 2F = about 80°. 



Optical orientation : plane of optic axes (010) ; Bxa = 7 ; 7 : a = 20° in obtuse 

 angle /3. Pleochroism in thick cleavage pieces: a light pink; ^, 7 nearly 

 colorless, with a faint ycllowsh tinge. 



A thermal examination of mixtures of the two phosphates was undertaken. 

 The results are stated in the following table: 



/25\ 

 after c. Density GM-j-j =3.058. Optical properties determined under the 



