Eakle.] 



Mineralogical Notes. 



317 



A mean of two analyses of the whitest mineral is: — 



Si0 2 . . . 

 Al 2 O a \ 

 Fe.A j 



53-40 



3-87 



CaO 

 Na 2 



H 2 0, ignition 



30.56 

 .7.61 

 .4.46 



99.90 



Datolite. — Veins of datolite are about as numerous as those of 

 pectolite in the rock and the two minerals frequently occur together 

 in the same fissure. Many small druses of clear, colorless datolite 

 crystals occur, and these furnished the best crystals for measure- 

 ments. One vein about six inches wide is composed of calcite, 

 pure white kaolin and datolite, intimately mixed, and some of 

 the datolite crystals in this vein reach a dimension of a half cen- 

 timeter in length and width. 



The orientation for datolite, chosen by Dana in his "System of 

 Mineralogy,"* instead of the one commonly adopted by the German 

 mineralogists, is the most natural one for these crystals, and is, 

 therefore, adopted here in the accompanying figures, using his axial 

 ratio also. 



Owing to the characteristic wavy and striated faces on the 

 crystals, the measured angles with the reflecting goniometer varied 

 considerably, but they served for the complete identification of the 

 forms, a total of nineteen being observed, as foil o v\ ; ■ — 



<r(ooi) 

 a(ioo) 

 m(i 10) 



o{ I 20) 



M(on) 

 £-(012) 



x{\02) 



k(io4) 

 £(102) 

 «(m) 



v { 1 1 1 ) 

 £(112) 



A(U3) 



00(116) 



<7(3i2) 



,5(121) 

 (i.I.lS)? 



*E. S. Dana, "System of Mineralogy," 1890, p. 502. 



2 



