BY C. A. SUSSMILCFI AND H. I. JENSEN. 177 



pletely envelops felspar crystals in an ophitic manner The soda- 

 amphibole occurs as mossy and feathery aggregates of grains, 

 and in minnte rods. It has the characteristic properties of 

 riebeckite. As an accessory we have needles of a yellow, highly 

 birefringent but feebly pleochroic mineral, which appears to be 

 wohlerite. 



Name : Riebeckite Wohlerite(?) Comendite. 



No.X.618. Compact whitish Trachyte. Loc. : south side of 

 Johnston's Pinnacle. 



This rock resembles the typical Conowrin trachyte of the Glass 

 House Mountains. 



Texture : hypocrystalline, hyalopilitic, with stellate (pseudo- 

 spherulitic) arrangement. 



Constituents : microlites of soda-sanidine; interstitial masses 

 of colourless glass; stout rods of agirine-augite, strongly pleo- 

 chroic in bluish-green, olive-green, and yellowish-green; chlorite; 

 secondary iron-ores, and occasional corroded magnetite grains. 



Name : Hypocrystalline ^girine-Trachyte. 



Nq.X.611. Aphanitic Trachyte. Loc: Norris's Paddock, 

 Spring Creek. 



Handspecimen : loose, compact specimen out of the tuffs; it 

 has a rhyolitic appearance, being banded through flow-structure. 



Texture : hypocrystalline; very fine and even-grained; marked 

 off into stellate groups of minute microlites so as to have a 

 pseudospherulitic (strahlenkornig) fabric. 



Composition ; the chief constituents are the felspar (sanidine?) 

 microlites and interstitial glass. The latter has a very low 

 refractive index, and is light grey in colour. Idiomorphic grains 

 of bluish-green segirine, and small rutile rods occur sparingly. A 

 common accessory is a yellow mineral elongated in the a direc- 

 tion, which coincides with crystallographic h : Bxa=it : b almost 

 coincides with the c axis. These properties, together with the 

 colour and pleochroism, are those of wohlerite. 



Name : Pseudospherulitic Wohlerite(?) Ali-trachyte. 

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