214 J. C. MOULDEN. 
Oy a CORDIERITE-BEARING ROCK rrom BROKEN HILL. 
By J. Cotzerr Movu.pey, A.R.8.M., F.G.s. 
(Communicated by E. F. Pittman, a.R.s.M.) 
(Read before the Royal Society of N. S. Wales, October 6, 1897.] 
WuHILsT engaged in collecting a series of rock specimens in the 
field, illustrative of the Broken Hill district, prior to making a 
number of rock-sections for microscopical investigation, I happened 
- to come across an exposure of rock, on the rounded and weathered 
surfaces of which some dark, irregularly-fissured crystals were 
apparent. After breaking hand-specimens of this material, I 
recognized the mineral as cordierite, and upon testing it chemically 
and microscopically, found that my field observation was confirmed. 
The occurrence of cordierite as a rock forming mineral, in a 
perfectly unaltered condition, has not, to my present personal 
knowledge, been yet noted in Australia, but whether it has or has 
not, I have ventured to hope that, from what I have subsequently: 
discovered, viz.:—that it has a somewhat extensive development 
in the metamorphic rocks of this district, the matter would be 
sufficiently of interest to geologists in this country, to warrant my 
bringing it under the notice of this Society. 
Cordierite—also variously known as iolite and dichroite—is 4 
silicate of alumina, iron, and magnesia, which crystallizes in the 
rhombic system. It occurs as a constituent of certain granites, 
gneisses, and granulites—notably in the granite of Bodenmais in 
Bavaria, It occurs, too, as the result of contact metamorphism, 
and as an original secretion from the magma in certain andesites. 
The clear transparent variety, found in Ceylon as rolled masses, 
is known as ‘saphir d’eau,’ and is cut and used asa gem. Where 
it occurs as a rock constituent, it alters somewhat easily to pinite 
and other ill-defined minerals, and in those forms is common in 
