329 
` The descriptions by Jack (? and Ransome (9 of the albite 
present in albitite rocks, described by them, strongly suggest 
the presence of chequer albite in these rocks. 
* (b) Quartz Albitite.—D'$, =2°640. This forms the most 
abundant type, and it is with this rock that the albite is 
associated. Here the quartz is present as blue opalescent 
grains as in the main granite. Microscopically, the minerals 
present are quartz, albite, and as accessories apatite, zircon, 
prismatic crystals a and, also, as geniculate twins (twinning 
plane LL01p, giving a sagenite networ 
The albite has a refractive index less than Canada Balsam. 
In asana perpendicular to the albite lamellae, the 
symmetrical extinction is 16° and on sections showing as 
untwinned the maximum extinction is 19° from the | 092) 
material. Muscovite is recognizable. Under the microscope, 
the minerals present are albite, muscovite, and accessorily, 
quartz, apatite, zircon, and rutile. 
e albite possesses the same charac teristics as in the 
other occurrences, and the peculiar chequer twinning is 
observed. 
Some of the mica is associated with quartz in little tufts 
and bilis Both mica and quartz are probably apte des 
Some muscovite, however, is undoubtedly pipe The 
has apparently suffered some change, due to the ehe pr 
mineralizers, but the results are not as clearly demarcated as 
in other examples 
A study of the literature of albite, aplites, or pt 
indicates = this type of rock is comparatively ra 
Rocks of this type were first described under the name 
albitite by Turner (9) from Plumas Co., Sierra Nevada. These 
aplites occur as dykes, and consist essentially of albite in 
granular aggregates. Quartz is occasionally War nan ape 
but may occur plentifully in the same dyke. 
or may not be present. Iron ores and as are sparingly 
distributed, and garnet is an occasional accessory. Dupare 
san L. Jack: Geol. aed S. Austr., Bull. No. 3, 1914, p. 16. 
9 F. L. Ransome: Journ. Wash. Acad. Sci., vol i., No. 4, 
i, ee. 114-118. 
(9 H. W. Turner: 17th Ann, Rep. U.S.G.S., pp. ne et seq. 
