which it is associated. It is evidently a mineral which derives its 
materials from various other minerals, the elements being re-com- 
bined into the more compact form of stanrolite under deep-seated 
conditions/ 7 
The densities and compositions of the four genetically related 
minerals Prochlorite, (Tloritoid, Stanrolite, and Almandine, are: — 
Mineral. 
Composition. 
Water. 
0 
T . Molecular 1 
Denai *-y- Volume. 
Proclilorite 
x 2 H 40 • 3 ( Fe. Mg) O-28i0,-h 
y 2 H 2 0 * 2 ( F e, M g ) 0 ( Af Fe ) 2 0 y * 
Si() 
‘0 
10 12 
2*95 1 14f 
Chloritoid ... 
H 2 0- (Fe, Mg) ()• (Al, Fe) 
®0 a 
0-7 
3*55 09 
•Stanrolite ... 
H 2 0- 2{f e,Mg)0* 5(Al,Fe).,0 3 . 
4Si() 2 
1-2 
3-70 122 
(or 244) 
Almandine ... 
3( Fe p Mg)0 (Al,Feh,0 8 ’ 
3SiO a 
none 
4*05 117 
From these figures one is led to the conclusion that temperature 
and pressure play a large part in determining which species is gen- 
erated by the metamorphism of a given rock containing the materials 
required. It is evident that at the lowest temperatures and pressures 
prochlorite would tend to form; at higher temperatures but mod- 
erate pressures, stanrolite. On. the other hand, at high pressures 
and moderate temperatures, chloritoid would develop, whilst at the 
highest temperatures with moderately low pressures, almandine gar- 
net would form. See Plate X'HSL 
The data for I elite, a very similar mineral found both in igneous 
and metamorphic rocks, are imperfect. Its water percentage may be 
1.5 or nil, and its molecular volume 227, 232 or 465. These figures 
point to a fairly high temperature and very low pressure as the 
condition conducive to its formation. 
Stanrolite in hand specimens has now been recorded from the 
following localities in the State: Mogumber and (Jreenbushes (S.W. 
/71 
Division), Mondoonfa, Mary River and Richenda River (Kim. l)iv.). 
Tn addition, microscopic grains have been observed in heavy sands 
from several localities in the South-Western Division, including* 
Freshwater Bay, Cape Deeuwin, Pemberton and Cheyne’s Bay. 
* Based 011 a constant ratio for all four minerals of three Fe" to one Mg', and on 
the assumption tint, the usual proportion of Fe'" is negligible. 
f Van 11 iso’s data for prochlorite, on p. 106 of his Metamorphism. require revision. 
Ills molecular weight 1,382*52 seems to be based on two wrong assumptions, viz., 
(1) that MgO is the onlv protoxide present, whereas as a. matter of fact FeO and MgO 
are usually present in about equal molecular proportions, (2) that the empirical formula, 
copied from Tsehermak, contains onlv two molecules, whereas it contains three of ser- 
pentine and seven of ameslite, a total of ten. These, molecules are not additive but sub- 
stitutive. The true mold ukir weight is therefore in the vicinity of 318, varying 
with the relative ratios of Mg to Fe, and of Sp to At. Ifis density 2-71 is too low, 
judging by the figures given by Dana : 2 *85 appears to he a better figure for a unit ratio 
of Fe to Mg. Finally, bis molecular volume, 509-210 is approximately five times too 
high, being dependent on the molecular weight and on the inverse of the density. 
Taking 318 for M.W. and 2-85 for density, the M.V. is 112. 
