CRYSTALLOBLASTIC ORDER AND MINERALS 515 



staurolite, cyanite — epidote, zoisite — pyroxene, hornblende — ^mag- 

 nesite, dolomite, albite, mica, chlorite, talc — calcite — quartz, 

 plagioclase — orthoclase, microcline. In general the series is one of 

 decreasing specific gravity and of increasing molecular volume.^ It 

 is interesting to compare Grubenmann's values for specific gravity 

 and molecular volume^ for the four minerals under dicussion. 

 They are: 



Ottrelite is an exception to Grubenmann's generalization. 



Mention may be made here of other references to crystallo- 

 blastic order. Wolffs has shown that ottrelite may crystallize out 

 before ilmenite. According to F. W. Clarke,"* andalusite, silliman- 

 ite, and kyanite originate in the order named, with increasing meta- 

 inorphism. This has been recorded by several observers. Van 

 Hise^ states that garnet represents a less advanced stage of alter- 

 ation than staurolite. Where both of these minerals occur in 

 the same schist garnet is frequently inclosed in staurolite. The 

 present writer has seen this in many of the New Hampshire schists. 

 Leith^ writes: "We know definitely that quartz generally crys- 

 tallizes before feldspar, and mica and hornblende before quartz and 



feldspar Muscovite and biotite, when they occur together, 



usually develop simultaneously Exceptionally the mus- 



covite evidently crystallizes before the biotite." Garnet and 

 staurolite are listed by Leith with the minerals that crystallize out 

 after the cleavage-making minerals. 



October 18, 1913 



^ Op. cit., pp. 91-92. ' Op. cii., pp. 54-55- 



3 J. E. Wolff, "On some Occurrences of Ottrelite and Ilmenite Schist in New- 

 England," Bull. Harv. Mus. Comp. Zool., XVI, 8 (1890), p. 163. 



4 "Data of Geochemistry," U.S.G.S., Bull. 330 (1908), p. 528. 

 s C. R. Van Hise, Treatise on Metamorphism, p. 903. 



* Rock Cleavage, pp. 93-94. 



