298 RECORDS OF THE AUSTRALIAN MUSEUM. 



On some specimens of OHIASTOLETE from BIM- 

 BOWRIE, SOUTH AUSTRALIA. 



By C. Anderson, M.A., B.Sc, Mineralogist. 



(Plate xlvii.) 



The Trustees of the Australian Museum have recently acquired from 

 Mr. G. R. Howden, by donation and purchase, some exceptionally 

 good specimens of chiastolite. In addition to those in the Museum, 

 I have been enabled, through the courtesy of Mr. E. F. Pittraan, 

 Government Geologist, and Mr. G. W. Card, Curator of the Mining 

 and Geological Museum, to examine some fine specimens in the 

 Survey collection. Mr. W. S. Dun, Palfeontologist to the Survey, 

 was also kind enough to lend me some specimens which he has in 

 his possession. All the minerals examined came from the same 

 locality, Mt. Howden, ten miles north of Bimbowrie, South Aus- 

 tralia. The crystals are distinguished by large size, they shew 

 the characteristic markings very distinctly, and some exhibit 

 features which, so far as I know, liave not hitherto been described. 



Chiastolite is a variety of andalusite, and is only distinguished 

 from it by the constant occurrence of carbonaceous or clay-slate 

 inclusions, disposed in the form of a cross. Andalusite and 

 chiastolite are characteristic of the metamorphic schists, and are 

 usually found in the contact zones of clay slates, near granites, 

 syenites, and diorites. The crystallographic system is ortho- 

 rhombic, the forms being very simple, usually shewing only (110) 

 and (001). The pattern of the dark inclusions seen on a cross 

 section varies considerably, even in different segments of the same 

 crystal, but two chief types are apparent — (a) The crystal has a 

 dark rhomb in the centre, the outlines of which are parallel with 

 the crystal boundaries, and, from the angles of this rhomb, dark 

 laminae pass to the prism angles of the crystal (nmcle tetragrammS 

 of Haiiy) ; (b) further the angles of the prism may be occupied 

 by four dark rhombs, corresponding in form with that in the 

 centre (made pentarhomhiqrie of Haiiy.) 



According to Mr. Howden, the Bimbowrie mineral occurs 

 either embedded in argillaceous schist, or as rolled pebbles, along 

 with quartz, jasper, aventurine, etc. Towards the surface, where 

 atmospheric influences are at work, the crystals are fairly easy of 

 extraction, and all the more perfect specimens obtained were 



