m 



Relations to zeophyllite ^j and other minerals. 



The only mineral to which gyrolite is somewhat closely 

 related is, as far as I can see, the zeopliyllite from Grosz- 

 Priesen^) and Alter Berg-^) in Bohemia. 1 shall in the 

 following give a short account of the properties of that mineral, 

 as far as they can contribute to clear up the relation between 

 it and gyrolite. 



The succession of minerals is very different in the two 

 zeophyllite localities; at G rosz- Priesen it overlies natrolite 

 and at Alter Berg it overlies calcite or hyalite and apophyllite 

 and is overlaid by hyalite; we thus see, that the occurrence of 

 zeophyllite is not quite similar to that of gyrolite, but as the 

 last named mineral varies somewhat in that respect it is not 

 possible to regard that fact as conclusive. 



The crystalline form is by Pelikan described as rhombo- 

 hedral with the base, a prism and a rhombohedron forming 

 an angle of almost 78° with the base; Cornc has not more 

 closely examined the mineral in that respect, upon a specimen 

 from Alter Berg in the iVluseum of Copenhagen 1 have, 

 however, found quite the same form. As the base is very 

 badly developed I have measured the angle between the prism 

 (of second order) and the rhombohedron and determined it to 

 31° 45' as a mean of 6 values varying from 31° 15' to 32° 05'; 

 from this the angle between the rhombohedron and the base 

 is calculated to be 79° 05', and if we assume that the rhom- 

 bohedron is s{022l} we get the axial ratio for the zeophyllite: 



с = 2-2451 

 while for the gyrolite : 



с = 1-9360. 



As the measurement of the angles are for neither of the 



M This relation is mentioned by Cornu: Centralbl. f. Min. 1906, p. 80. 

 •-') Pkijkan: Sitzb. d. k. Aiiad. d. Wiss. Wien, 111, 1902, p. 336. 

 ^) CoHNu: Tschermalis Min. und Petr. Mitt. 24, 1905, p. 127. 



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