96 
Rex T. P rider. 
of a good 001 eleavag(‘ and poorer 100 cleavage, are almo.st indistinguislmhle 
from the grossularite under ordinary light. The refractive index /3 clos(‘ to 
1 • 765, extinction Z /\ 001 cleavage 30°, y-o approximately -042 and neg- 
ative optical character, indicate an epidote with approximately 15 per cent 
(Winchell. 1933, p. 313). TIichc skc'letal crystals often enclose idioblastic 
grossularite. 
Diopside is not so abundant. It is a pale greenish variety in hand sp(‘ci- 
men, colourless in thin section. It occurs in a similar fashion to epidote, 
enclosing grossularite. The greater part of the diopside is confined to the 
quartzose portions of the rock, where it is idioblastic towards the (piartz. 
Sphene is an abundant accessory in cloudy irr(‘gularly shaped allotrio- 
morphs usually surrounded by gariif't. Accessory opacjue iron or(‘ occurs 
in several bands. 
Quartz, the only other constituent, occurs in elongat(‘d xenoblasts and 
skeletal grains between the garnet ciystals. There are no signs of any sti-ain 
in the (piartz. 
The crystalloblastic order is : spliene, grossularite, (‘pidote, diojxside, 
and (juartz. The microstructures are shown in figure 6A. An analysis of this 
rock, quoted from Sim})son (1937, p. 32) is 
SiO., ... 
TiOa 
AhO. 
FeaOs 
FeO ... 
MnO 
MgO 
CaO ... 
Alkalies 
H.O+ 
H2O- 
50 • 68 
0 - 96 
12-63 
3-79 
2-13 
1 - 02 
1 -71 
26-81 
Tr. 
0-35 
0-26 
100-34 
Judging from its high lime and alumina and absence of alkalies the j-ock 
was originally an impun* siliceous and argillaceous limestone. The C’aO, 
AI2O3, and SiO., liave given grossularite, the entrance of some Fe20;3 has letl 
to the developna^nt of epidote and the C'aO with the small amount of MgO 
has given rise to diopside. The source of the titanium of the analysis is spheiu', 
of which there is a small amount in the rock. 
The hornblende-diopside quai'tzites are represented by a numb('r of 
.specimens in the collection of which 15405 shows all the charact(a‘istic feature's. 
Megasco])ically, it is a coarse-grained, dark green (juartzite. Under the micro- 
scope, it is (‘ssentially a coarse granoblastic aggn'gate of ejuartz grains (2 3 
mm. diameter) which carry poikiloblastic inclusions of pale greenish diopside^ 
(Z/\c 42° indicating the presence of some iron) and greenish amphibole, 
Aggi‘ogat('S of diopside, hornblende, grossularite, and a little carbonate occur 
between the quartz grains. The (piartz (70 per cent of the rock) is xeno- 
blastic towards all other constituents. It is all considerably strained and 
carries minute gas-li(piid inclusions. 
The amphibole, occurring in pale greenish .sheaf-like aggregates, ajip('ars 
to be developing from the diopside which is occasionally seen as relicts in the 
amphibole prisms, d'he chai’acters of this amphibole are : — 
Pleochroi.sm X pale yellow-green ; Y deep olive green ; Z bluish- 
green. 
The absori>tion is Y>Z>X and Z/\c = 19°, indicating that it 
is blue-gret'ii hoj'nblende rather than actinolite. 
