Chap. V. ] 
RHODONITE. 
139 
p. 166, (1868), as near Maukulam, about 11 miles N.-E. of Madura. 
Balfour's list also gives a second locality, namely Manapara. 
Rhodonite. 
This mineral is a pyroxene belonging to the triclinic system. It is 
a metasilicate of the composition represented by the formula MnSi03, 
which corresponds to a theoretical maximum % of manganese of 41-86. 
Frequently a small portion of the manganese is replaced by iron, 
calcium, or magnesium, and in rare cases by zinc. When these 
replacing constituents reach considerable proportions then a different 
name is sometimes given to the minera'. Thus when high in lime the 
mineral is called bustamite_ and when high in zinc it is known 
as fowlerite. A separate name has not been given to the variety high 
in iron, whilst rhodonite containing large quantities of magnesia has 
not yet been recorded. The characters as given by Dana in his ' System 
of Mineralogy ', page .379, are as follows : — 
Found either in crystals or massive, or as embedded grains. Cleavage 
Character^ perfect, prismatic (m and M) ; c less 
perfect. Fracture conchoidal to uneven ; 
very tough when compact. H. = 5-5 to 6-5. G. = 3-4to 3-68. Lustre 
vitreous ; on cleavage surfaces somewhat pearly. Colour light brownish 
red, flesh-red, rose-pink ; sometimes greenish or yellowish, when 
impure ; often black outside from exposure. Streak white. Transparent 
to translucent. 
Under the microscope the mineral is colourless and shows well- 
marked prismatic cleavages appearing as 
ilicroscopic aspect. , . . , , , . 
two series crossmg at angles approaching 
a right angle {mM = 92° 28^') in sections at right angles to the vertical 
crystallographic axis (see fig. 3, Plate 12), and as a series of parallel 
traces in sections parallel to the vertical axis. With regard to these 
parallel cleavage traces the extinction is very variable and usually very 
obhque. Dana does not mention any cases of twinned crystals of 
rhodonite. I have not yet seen any Indian specimens of rhodonite 
exhibiting definite crystal faces and consequently have not in this way 
recognised any cases of twinning. Under the microscope, however, I 
have not infrequently found examples of this mineral showing well- 
marked twinning, this being sometimes polysjTithetic. Rock sections 
from Asalpani (Bhandara district), Devi (Chhindwara district), Jothvad 
(Narukot), and Manegaon (Nagpur), exhibit this phenomenon. In the 
