22 Kraus and Cook — Datolite from Westjield, Mass. 



prism. Rammelsberg,* in establishing the isomorphism be- 

 tween datolite, gadolinite, and enclase, accepted the position 

 proposed by Dauber but made g (fig. 1) the unit prism, whereby 

 the ratio was reduced to 



0-6329 :.l : 0-6345. 



Groth,f Liweh4 Goldschmidt,§ and others have accepted 

 these values. Hintze| accepts the statement of Liidecke^f that 

 this position is the more natural and gives the simpler indices. 

 Liidecke's argument, moreover, loses its force when we con- 



sider that seventeen of the thirty new forms described by 

 him were afterwards shown by G-oldschmidt"** to belong to 

 anglesite and not to datolite. Dana, ft however, does not accept 

 the above position, but follows Levy^J and interchanges the 

 a and c axes. In so doing the values obtained by Dauber are 

 taken, so that the ratio adopted by Dana is : 

 a: 6:c=0-63446 :1 : 1*26574. 



We agree with Dana that this position permits of a more 

 natural interpretation of the crystals and also affords the 

 simpler indices. This position is, therefore, the one accepted 

 by us. As indicated by Dana,§§ the isomorphism existing 

 between datolite, gadolinite, and euclase can be shown by this 

 position just as well as by the one adopted by Hammelsberg. 



The four types of development already referred to may be 

 described briefly as follows : 



Type one (fig. 1), as noted by Whitlock, is the predomina- 

 ting habit. Thirty-four crystals were found to possess this 



*Zeitschr. der Deutsch. Geol. Ges. xxi, 807. 



f Tabellarische Uebersicht der Mineralien, 1898, 116. 



JZeitschr. fur Krystallographie u. s. w., vii, 569, 1883. 



§ Index der Krystallformen der Mineralien, 1886, I, 485. 



|| Handbuch der Mineral ogie, II, 164. 



l|Zeitschr. fur Naturwissenschaf t, lxi, 235-404, 1888. 



**Zeitchr. fin- Krystallographie, xviii, 280, 1890. 



ft System of Mineralogy, 6th edition, 1892, 504 and 505. 



%X Loc. cit. §§ Loc. cit. 



