THE ANALCITE BASALTS OF SARDINIA 747 



Elsewhere^ Doelter speaks of an olivine of Scano, of which Ippen 

 made an analysis (not given). It is stated that the results of 

 this correspond to the composition 7(Mg2Si04) • 3(Ca2Si04). This 

 would be a most extraordinary olivine, unique in mineralogy, and 

 almost corresponding to a monticellite, although occurring in an 

 igneous rock. But unfortunately the analysis has never been pub- 

 lished, and one does not even find it in the elaborate Handbuch der 

 Miner alchemie of Doelter, either under monticellite or under olivine. 

 Regarding this olivine. Professor Doelter has been kind enough to 

 write me (December 31, 1907) that it is white, forming isolated 

 grains, and not in granular nodules like the olivine described above. 

 He says that its locality is near Scano, that it is very rare, and that 

 it has nothing in common with the olivine of the nodules. 



The nodules of augite are subangular and smaller than the 

 others, from i to 5 cm. in diameter. They are very compact, not 

 granular, each one made up of a single crystal of the pyroxene, often 

 twinned, and more or less split up through cleavage. The pyrox- 

 ine is greenish-black, and it seems to be free from inclusions. An 

 analysis gave me the following results: 



SiOa 50.13 NiO , 0.02 



TiO^ 1. 91 MgO 13.73 



AlA 7.08 CaO 20.06 



FeA 1 . 10 Na^O i . 88 



FeO 4.41 K2O 0.25 



MnO 0.05 H2O o.ii 



100.73 



Its chemical composition will be discussed later, when its optical 

 properties shall have been studied. 



Chemical composition. — 'Analyses made by me of three of these 

 basalts are here given (Table II), along with several others of 

 related rocks. 



The three analyses of Sardinian basalts resemble each other 

 quite closely in their general features. As regards most of the 

 constituents, they are not specially noteworthy. Silica is rather 

 low for basalts, and titanium is high, the latter a feature common 



^ C. Doelter, Phy. Cheni. Miner. (1905), 64. 



