128 
MEMOIRS OF THE QUEENSLAND MUSEUM. 
Chemical Analysis. 
A proximate analysis of this sample has given the following result : — 
Moisture at 105 deg. C. . . . . . . 1-1 % 
Volatile Matter . . . . . . . . 75-7 % 
Fixed Carbon . . . . . . . . . . 144 % 
Ash . . . . . . . . . . . . . . 8-8 % 
Chemically this indicates a good medium-grade to high-grade torbanite. 
The high percentage of volatiles is due to the large quantity of algal material 
present, while the low ash content reflects the small amount of mineral matter 
in the rock. As is the case with all melanocratie torbanites the ratio of volatiles 
to fixed carbon is less than 10 to 1. 
CARNARVON CREEK TORBANITE. 
General and Macroscopic. 
Locality of sample chosen for study: Outcrop in southern gully on 
portion 2, parish of Aubrey, county of Consuelo, about half-a-mile east of 
Carnarvon Creek, approximately 120 miles north of Injune. Geological Horizon: 
Upper portion of Upper Bowen Series. Age: Upper Permian. 
In the hand specimen this is a fine-grained, homogeneous rock of black 
colour. It cleaves fairly readily along the bedding, and breaks with a hackly 
fracture. It has a dull lustre and gives a dull greyish-brown streak. The 
specific gravity is 1-30. Apparently it is resistant to weathering, as the specimen 
studied shows no evidence of atmospheric weathering more than three millimetres 
from the exposed surface. It ignites fairly readily and burns with a bright 
flame, giving a waxy, aromatic odour. Tiny scales of gypsum arranged in 
small patches occur at intervals along the bedding planes. 
From the above physical properties, adopting Dulhunty’s (1943) 
classification, the hand specimen is identified as a low-grade, dull melanocratie 
torbanite. 
Microscopic. 
In thin section the rock shows the uniform microscopic structure 
characteristic of a torbanite. This consists of translucent gelosite and retinosite 
bodies, separated by films of opaque, matrix. The percentages of these 
translucent bodies in the rock, determined by means of the eyepiece micrometer, 
have been found to average 42 % gelosite and 3 % retinosite. This places the 
rock just over the borderline between a low-grade and a medium-grade torbanite. 
As in the Alpha torbanite these translucent bodies are disc-shaped, and 
appear elongated in the vertical section and roughly rounded in the horizontal 
section. However, they are much smaller in their average size than those of 
the Alpha torbanite, the diameter of most of them being only 0-15 mm., and 
there is also much less variation in their size. They have fuzzy, indefinite 
margins and, in the horizontal section, present a botryoidal appearance. 
Under ordinary transmitted light the gelosite is pale yellow in colour, 
and the retinosite orange-yellow. They both exhibit the characteristic optical 
properties as described above for the Alpha torbanite. Both the gelosite and 
the retinosite bodies also have been replaced to a small extent by chalcedony, 
but the degree of silicification is less than that in the Alpha torbanite. 
