1892.] Mineralogy and Petrography. 5,3 



Brazil, examined by Derby, disclosed the presence of this accvs>orv, 

 which is thought by him to be as constant a constituent of those rock* 

 as any mineral save zircon. Experiments made with granites from the 

 United States seem to indicate the value of the pan as a petroirraplncal 



— The rare blue hornblende riebeckite i- reported by Cole' in three 

 pebbles found in the drift of North England and of Wales, in addition 

 to its occurrences in the microgranite of ftfynydd Mawr, where it was 

 discovered by Harker and Bonney a few years ago. 



Mineralogical News. — General. — Since manv of the supposed 

 paramorphs recent years to be due not to the mo- 



lecular rearrangement of material already existing, but rather to the solu- 

 tion of some original substance and its replacement by a new deposition, 

 Bauer 2 has re-examined the pseudomorphs of rut He after brookite from 

 Magnet Cove, Ark., to determine whether or not the substance is a true 

 paramorph. After studying many thin sections of the brookite, rutile, 

 and intergrowths of the tw T o, he concludes that the latter are true para- 

 morphs, the rutile originating in a molecular re-arrangement of the 

 Ti0 2 . The rutile begins to form on the exterior of the brookite crys- 

 tals, or along cracks in them, as needles penetrating the brookite sub- 

 stance. The rutile pseudomorphs after anatase from Brazil, the Urals 

 and other' localities, are also declared to be true paramorphs. The 

 same author has also re-examined the Michel-levy ite of Lacroix, which. 

 Dana declared to be barite, and finds that Dana's statement is correct 

 The axial angle is large, but it cannot be measured, as the acute bisec- 

 trix does not enter the field of view. The mineral differs from or- 

 dinary barite only in the possession of a very perfect cleavage in the 

 direction of one prismatic face. On the base it shows twinning striations 

 resembling those of plagioclase. The twinning plane is the prismatic 

 face parallel to which is the most perfect cleavage. The structural 

 peculiarities of the Perkin's Mill barite are all due to this abnormal 

 cleavage, which in turn is dependent upon the twinning, which is new 

 to the mineral, and is probably the result of pressure. Measurements of 

 druse crystals of the same substance yield the forms cha 

 barite and the new plane A P^ with a: b: C-—.8152 : 1 : 1 

 mineral associated with calcite and phillipsite as druses oi 



