Appendix O] SPECIMENS OF ROCK AND SAND Io61
by the green variety which marks its first stage of alteration ; but these are almost constantly associated with an abundance of colourless epidote and muscovite, the products of its complete transformation.
Zircons are rare, but when present in the biotite are surrounded by a faint pleochroic halo, the radius of which does not exceed .017 mm.
From Sai, six miles SSE. of C. civ; strike ESE.—
WNW., dip 75° NE. (0 t2 and 015) quartz; (013) quartz schist, no doubt part of a mica schist series; (014) granite.
12. Near dry riverbed of Kuruk•daryä. Ap&te 1
A small worn angular fragment of a red quartz felspar rock.
12 a. Kum•Kuduk, 8 miles NW. of. Rock-salt.
Irregular nodules, some consisting of rock-salt encrusted with sand, some of sand cemented with rock-salt.
TERMINAL COURSE OF ETSIN-GOL RIVER
Mao•mei (or). Hornblende Andesite.
A closely jointed dark grey, almost black, rock with small phenocrysts. Sp. gr. 2.73.
The ground mass is difficult to analyse : it consists of irregular areas of felspar crowded with minute granules and needles, some if not all of which are hornblende.
The phenocrysts are idiomorphic crystals of hornblende, plagioclase, and magnetite. The plagioclase is glassy clear, often either zonal, or with undulose extinction. Its optical properties and specific gravity show that it ranges from andesine to labradorite.
The hornblende is defined by the forms (t ro), (oio), and (zoo) ; it extinguishes at 19° and its pleochroism is, X, from colourless to faint yellow; Y, brown; Z, also brown, but of a darker shade.
Biotite is represented by a few rare phenocrysts which present reaction rims of hornblende and magnetite. In one case biotite forms the core of a crystal of plagioclase and some of its cleavage lamella penetrate the felspar running parallel to the planes of albitic twinning.
Apatite is fairly abundant, especially in association with the biotite : some sphene is present and a little, almost colourless but slightly pleochroic, epidote.
Mao-mei (02). Granite.
A rather coarse reddish, consisting of a mosaic of quartz, hypidiomorphic crystals of felspar, biotite, and muscovite.
The quartz contains abundant liquid cavities, isolated fragments of biotite, muscovite often in small crystals which may be grouped in clusters, and numerous granules which appear to be the remains of some incompletely digested mineral, probably felspar. The liquid cavities form long linear series which run in one prevalent direction and sometimes cross from one element of the quartz mosaic into another.
The felspar consists of orthoclase, more or less perthitic,
microcline, and a plagioclase which appears to be an albitic oligoclase.
The biotite is brown and strongly pleochroic : X, straw yellow ; Y and Z, deep brown to black. It contains crystals of zircon and apatite; the former surrounded by pleochroic haloes.
The muscovite is both primary and secondary. When primary it sometimes corrodes the biotite and completes its growths, the cleavage planes of the two maintaining a strict parallelism.
14 a. (03). A worn fragment. Quartz.
Mao•mei (o4). Quartz Hornblende Schist.
This well-foliated green schist consists of quartz mosaic, plagioclase felspar, and parallel foliae of hornblende. Associated with the hornblende here and there is a brown biotite, the cleavage planes of which also lie approximately in the plane of foliation. A good deal of apatite, magnetite, and some isolated crystals of epidote are also present.
The hornblende is grass green in colour and strongly pleochroic : X, faint straw yellow ; Y, dark green ; Z greenish blue. Its angle of extinction is 24°.
The pleochroism of the biotite is, X, faint yellow, like the hornblende ; Y and Z, deep brown.
The quartz mosaic includes abundant andesine in individuals which sometimes acquire a comparatively large size. In some cases the felspar is shot through with threads of quartz. The apatite also occurs in large crystals or rounded grains.
The eyes formed by an expansion of the clear quartz mosaic resemble those described later in the hornblende schist (72) of Mirân, but contain in some cases as an additional mineral a faintly pleochroic almost colourless epidote. It often lies in the middle of an eye and is bordered by a fringe of small fragments which have been detached from it. In some cases a whole crystal has been resolved into a heap of small grains.
16. Chin•êrh•ch'üan, Pei•shan (or 3). NW. of Mingshui, from ridge one mile SE. of Chin-êrh-ch`üan.
Breccnated Rhyolite. A compact, jointed, chocolate-coloured rock with small lighter coloured inclusions. The joint surfaces are covered with a black lustrous patina.
It consists of a finely granular, colourless, glassy basis, through which are scattered angular fragments and splinters of quartz, broken crystals of orthoclase, and oligoclase. Immersed in this are small fragments of rhyolite with marked flow structure. These, which are themselves fractured, and differ in details from one another, form the greater part of