Chap. XVI.] 
GONDITE SERIES : PETROLOGY. 
339 
has been found at Chargaon. In these coarsely crystalUzed varieties 
the garnet varies from bright yellow to orange and orange-red. 
An examination of sections of gondite under the microscope some- 
times shows that apatite is present in considerable 
Apatite.gondite. abundance. The rock can then be designated apatite- 
gondite. This variety is not, however, common, and no example has yet 
been found in which the apatite is conspicuous in the hand-specimen. 
Less common than gondite and spessartite-rock are those varieties 
The rhodonite-hear- gf series characterized by the presence of rho- 
ing members of the - -iii i- 
series. donite m considerable or predominant proportion. 
Of these the most abundant is a rock composed of a mixture of spessar- 
tite and rhodonite with or without quartz. The rocks containing rho- 
donite are never so fine-grained as the typical gondite. When composed 
entirely of rhodonite, or nearly so, they have a saccharoidal appearance 
resembling that of a crystalline limestone, although the colour is, of 
course, not white, but rose-pink when fresh. Under the microscope this 
rhodonite rock appears as an aggregate of roughly equi-dimensional cry- 
stals ; they are allotriomorphic in outline owing to the fact that they 
are pressed one against the other, except that there is a tendency for them 
to be somewhat elongated in the direction of the well-marked prismatic 
cleavage. A photo-micrograph of such a rock is given in Plate 12, fig. 3. 
More frequently, however, the rock does not consist entirely of rhodonite, 
but contains spessartite in either small or large proportion. When in 
small proportion the spessartite appears in the hand-specimen as rich 
orange-coloured rounded granules or crystals set in the pink rhodonitic 
matrix, the whole forming a most beautiful combination. In this rock 
the spessartite is often idiomorphically developed, sometimes as almost 
perfect trapezohedra, which are occasionally glass clear and then of the 
beautiful rich orange colour mentioned above. Under the microscope 
it is seen that the garnet is as a rule idiomorphic towards the rhodonite, 
which tends to enclose it. The proportion of spessartite may increase 
until it predominates over the rhodonite. In this case also the garnet 
tends to be idiomorphically developed with regard to the rhodonite, 
although in one or two cases I have noticed under the microscope more 
or less rounded crystals of rhodonite enclosed in the spessartite. In two 
cases I found this rhodonite-spessartite-rock to 
Barytes in the gon- contain a third constituent, of white colour, 
which was found on testing to he barytes. This con- 
stituent had every appearance of being an original constituent of the rock 
U H 9 
