262 



Mineral Notes 1 

 By D. Mawson, D.Sc. 



[Read August 10, 1916.] 

 Plate XXXI. 



Contents. 



1, Octahedrite. 2, Twinned Gypsum Crystals. 3, Beryl . 

 4, Loadstone. 5, Monazite. 6, Cordierite. 7, Sillimanite. 8.. 

 Spinel. 9, Spliene. 10, Davidite. 



1. Octahedrite. — A new and interesting locality for this 

 mineral is at the Glen Osmond Quarry, Adelaide. It is the- 

 first reported occurrence of octahedrite in Australia. The 

 crystals, which are of rare occurrence, are found on the drusy 

 surfaces of fissures traversing the quartzite. It appears in 

 acicular and obtuse octahedral forms associated with rutile. 

 The crystal measured is a stumpy octahedron about 1 cm. long. 

 It is capped by a basal face, and shows also the following : 

 (117), (113), (112), (111), and (110). The faces gave sharp, 

 readings. The angle of 68 c 15' between the cleavages is 

 characteristic. The colour is reddish-brown. The specimen 

 measured was collected by Mr. A. C. Broughton. 



2. Twinned Gypsum Crystals. — Mr. F. Voss Smith, 

 manager of Block 14 Mine, Broken Hill, handed over to me- 

 the interesting twinned gypsum crystals illustrated (see plate 

 xxxi.). They were formed in the interior of a boiler of 

 marine type on the Westward Ho ! Mine, near Manna Hill, 

 South Australia. The water which had formed the feed for 

 the boiler was drawn from a creek containing mineralized 

 water. When it w T as cleaned out, the occasion of the finding 

 of the crystals, the boiler had been standing idle for five 

 years and the contents evaporated. As shown in the illus- 

 tration, they are cruciform penetration twins, with the (100) 

 as twin plane. 



3. Beryl. — This mineral occurs in notable quantities as 

 large isolated crystals in the quartz reefs and coarse pegma- 

 tites associated with Pre-Cambrian granite intrusives out- 

 cropping to the north of Olary, in the Boolcoomatta Hills, 

 and elsewhere in that neighbourhood. They are faintly 



(l) These notes are based on minerals exhibited before the 

 Society during the years 1910 and 1911. Publication was deferred 

 owing to the author having mislaid his notes before departing on 

 his Antarctic Expedition in December, 1911. 



