32 
THE CRANBOURNE METEORITES 
distinguishes it from both. Unlike schreibersite, it is negative 
to both nitric acid and potassium hydroxide, but with hydrochloric 
acid it effervesces slowly, the bubbles rising from the numerous 
cracks; and this distinguishes it from the rhabdite, which gives 
negative results. 
The chemical composition of the four phosphides has been 
discussed in connection with the Pakenham meteorite (Edwards 
and Baker, 1941), and will not be repeated here. 
Pyrrhotite and Troilite 
These minerals occur only in the nodules. Both are creamy- 
brown in colour and strongly anisotropic, and they can be 
distinguished from each other only by their different etching 
behaviour. With nitric acid the surface of pyrrhotite is tarnished 
but washes clean, whereas troilite effervesces vigorously with the 
evolution of hydrogen sulphide. Hydrochloric acid fumes tarnish 
the surface of pyrrhotite but the acid does not otherwise affect 
it, whereas troilite effervesces vigorously with this acid and 
is stained brown. Of the other reagents, potassium cyanide, 
ferric chloride and mercuric chloride give negative results, while 
potassium hydroxide stains both brown. 
Of these minerals pyrrhotite is more commonly present in the 
nodules than is troilite. The sulphides may form the whole of a 
nodule core, or they may be intergrown with graphite, when the 
proportion of graphite tends to be greater near the margin. 
Graphite 
Graphite was found chiefly in the nodules, but some occurs as 
flakes or patches in the limonitic coatings of the meteorites. In 
polished section it is strongly anisotropic in brownish-grey colours 
and is pleochroic. It is soft, brittle, inert to all etching reagents, 
and marks paper. 
Oxidation Products 
Many fragments of scale removed from the meteorites consist 
of unreplaced remnants of nickel-iron, sometimes several milli- 
metres in diameter, cemented together by limonite. Such fragments 
have a hackly fracture, and when polished look like an iron- 
limonite breccia. Other pieces of the scale are sheet-like or 
lens-shaped, and consist essentially of limonite showing colloform 
banding. The limonite is studded with minute prisms and rhombs 
of rhabdite, indicating that the limonite has replaced the iron 
in situ. No trace of the schreibersite-B veins remains, so that 
presumably this mineral is destroyed by the lawrencite that the 
meteorites exude. 
