Chap V. ] 
SCHEFFERITE AND URBAXITE. 
133 
series (in Jhabua and Xarukot, in Central India and Bombay, respec- 
tively). As the rocks in which they occur show considerable variety as 
regards composition, it seems probable that the brown p\Toxenes con- 
tained therein will also be found to varv considerably lq composition and 
consequently in physical properties. In no case have I yet been able to 
carefully examine these p\T:oxenes either chemically or physically. In 
the case of the Vizagapatam examples, however, this would not be a 
matter of great difficulty, as the granules of the minerals are often of 
sufficiently large size for their extraction to be a matter of comparative 
ease. In the case of the igneous rocks containing these p^TOxenes in 
the Central Pro\'inces their separation for examination would also be 
fairly easy : but in the metamorphic rocks it would be quite another 
matter ; for the pyroxenes usually occur in small granules very 
intimately associated with the other constituents of the rocks in which 
they occur, so that they are not as a rule conspicuous in hand-specimens. 
As far as I can tell from the published literature available, these 
. . minerals wiU probablv be found, at least in some 
Composition. 1. i i • i 
cases, to correspond more or less closely with 
already-described varieties of pvroxene. In most cases I have not 
proved that these minerals contain manganese ; but considering the fact 
that they occur in manganiferous rocks and that those examples I have 
tested have given reactions for this element, sometimes weak and some- 
times marked, it seems probable that they are all more or less mangani- 
ferous. There are two known varieties of pyroxene that are both 
manganiferous and of brown and yellow tints. These are schefferite 
and urhanite. The composition of these two minerals is shown below : — 
Schefferite . . . (Ca,Mg)(Fe.Mn)(Si03)3 
Urbanite . . . (Ca,Mg)Si03 - 2NaFe ' (Si03)2 
(diopside) (acmite) 
In two analyses of the latter mineral i, r73 and 6"71 per cent, of 
„ . „ . , MnO are returned, the MnO presumably replacing 
bchefEente and urbanite. . , . , i r , 
some of the protoxides m the above formula. 
Analyses of schefierite quoted by Dana show 6 20 to 8"32 per cent, of 
MnO. The essential dii5erence in composition between the two minerals 
seems to be that urbanite, in addition to containing the ordinary 
molecule in which the oxides are all protoxides, as in diopside and 
schefierite, also contains the acmite molecule, in which a con- 
siderable proportion of soda is accompanied by ferric iron. Hence, as 
1 R. JIaufielieus, quoted by Sjogren. Bull. G. In.,t. Vp ala, II, p. 77. 106, (1894), [Dana]. 
