96 B. KOTÖ. 



It is generally supposed that the occurrence of glaucophane in 

 eruptive rocks is exceptionally rare. The mineral glaucophane, says 

 Rosenhusch,* appears exclusively confined within the formation of 

 crystalline schists, and phyllite. " Als Ausnahme f ist das Auftreten 

 in einer Minette der Gegend von Wackenhach in Breuschthal za 

 erwähnen." Therefore, it may be of some interest to give a short 

 description of it. The rock itself appears dark grey, and contains 

 small amygdaloidal cavities filled with the carbonate of lime. 



Under the microscope thin slides show a typical eruptive charac- 

 ter, but the decomposition has so far advanced that the fresh porphy- 

 ritic pyroxene is nowhere visible. The whole groundmass is made up 

 of a trichitic substance exhibiting a skelet-like arrangement. (Fig. IV.) 

 The glaucophane in this rock is surely of a secondary origin, as it 

 contains still remnants of a brown pyroxene in the centre. The 

 colour of this glaucophane is a light indigo-blue with a slight tinge 

 of purple. Sometimes amygdaloidal spaces are filled with radiating 

 needles of the same mineral. In all other respects it differs in no 

 wise from those already described. 



Before leaving the subject it may be well here to make some 

 remarks on the difference between the primary, and secondary glauco- 

 phane; and furthermore, on a probable mode of procedure, by which 

 the latter has been derived from the former. 



As to the distinctions of both, the crystallographic forms are 

 most apparent; the primary one is bounded by the prism together 

 with the clinopinacoid, while in the other, the above pinacoid is lacking. 

 Secondl}^, the primary mineral is considerably large in size of individ- 

 uals. One more difference still exists, and this is in colour; the 



* Miltroskopisclie Pliysiographie, I Baud, 2te Auflage, p. 471. 



t The writer may aid one more exception of its occurrence in Enrope. Lossen mentioned 

 its presence in an acidic eruptive rock in the Devonian, near the biisiu of Eibiugerede, in the Harz 

 Mountain. Here unfortun itely, the veteran-geologist does not give the exact description of it 

 25eitschrift d. deutch. geol. ües. XXXIII, 1881, p. 175. 



