Pf'troloc/f/ and Geologt/ of Queenstowii J)isfrirf. 125' 



quartz, are ortliDe-lasf. Cukulating- the percentage of t'elspai's fi-oju 

 the clieniical analysis, aceorilin<j: to the xVnierican ntethod, we get 

 the following result : — 



Orthoclase, 10.01%. 



Albite, 21.48%. 



Aiiorthite. :n.69%. 



Quartz is interstitial, and oeeurs in irregular shaped, pellucid 

 grains characterised by fairly abundant Huid inclusions containing 

 bubbles, llnienite is farly common, and is present in skeletal and 

 malformed crystals, occasionally showing hexagonal outlines. It is- 

 associated frequently with its replacement product, leucoxene, and 

 the triangular parting is often rendered very evident by relict 

 ilmenite bars surrounded by leucoxene. Extraction of any magnetic 

 particles from the powdered rock by a weak l;>ar magnet, showed 

 that only an inappreciable amount of magnetite was present. 



The accessory minerals include apatite, and zircon ; the latter 

 in chloritic areas is often surrounded by pleochroic haloes. 



Of the secondary minerals, chlorite is the most abundant, and is 

 usually intimately .associated with hornblende and epidote. It is 

 undoubtedly secondary after hornblende in nearly all cases, and '. 

 occasionally idiomorphic outlines of the latter mineral are preserved' 

 in the chlorite pseudomorphs. The chlorite is of the variety pen- 

 nine, giving ultra blue polarisation colours. It is decidedly pleo- 

 chroic X — Y, apple green. Z. yellow, and is microspherulitic in 

 part. Slightly yellow coloured grains of epidote. referable to 

 pistacite. almost invariably accompany the chlorite derived from 

 the hornblende. Some of the epidote is present as radial aggregates. 

 Fibres of a colourless mineral, having a refractive index between 

 that of chlorite and epidote. and exhibiting very high polarisation 

 colours, are probably calcite. It appears the most of the mag- 

 nesia, and part of the iron of the original hornblende,, have gone 

 to form chlorite, and the lime and the other portion of the iron, 

 with some alumina and water, have yielded epidote. Carbonate 

 occurs generally in massive cleaved, and twinned plates, filling 

 interstices between the quartz and the felsj^ar. It does not occur 

 replacing these minerals or the hornblende to any marked extent. 

 Notew-orthy is the fact that it differs very markedly from the meta- 

 somatic granular and dusty carbonate so commonly developed in 

 these rocks, as a result of hydrothermal vein alteration. A little 

 sericite replaces plagioclase, especially along cleavage planes. In 

 all sections examined a little sulphide is present, shoAving marked 



