BY H. I. JENSEN. 881 



Order of consolidation : felspar needles frequently penetrate 

 some distance into augite crystals but never to the core. 



( Magnetite 



Thnenite 



Olivine 



Apatite 



Felspar 



(Analcite when present) 



Name: Ophitic Olivine Dolerite or Diabase. Magmatic name, 

 Kentallenose (see Tables i. and ii.). 



Closely allied to N.17 is a rock from the Alpha (Diamond 

 Mine, Bullawa Creek, 13 miles N.E. of Narrabri, N.S.W., of 

 which the following description has been supplied to me by my 

 old friend, Mr. G. Saunders, B.E. 



Handspecimen resembles a basalt, being of a dark colour and 

 moderately fine-grained. It occurs as a dyke about 8 feet wide. 

 Bands of calcite occur in it, and due to these bands the rock 

 crumbles away on exposure. It intrudes sandstone, and capping 

 these rocks there is an alluvial deposit in which diamonds, 

 sapphires, zircon and gold have been noticed. 



Microscopic Description. — Texture holocrystalline ; grainsize 

 medium with a few large phenocrysts of augite and plagioclase; 

 fabric caraptonitic and ophitic. 



Constituents in order of decreasing abundance are (1) felspar, 

 (2) titaniferous augite, (3) colourless diopside in phenocrysts, 

 (4) olivine, (5) serpentine, (6) magnetite, (7) grains of red olivine 

 (fayalite), and (8) apatite. 



I have examined a slide of it sent to me by Mr. Saunders, and 

 I find it to be a rock closely related to N.17. The felspar is a 

 basic labradorite, and it as well as the olivine and augite occur 

 in two generations. 



