30 
THE CRANBOURNE METEORITES 
Mineral Composition 
As would be expected from their chemical composition, the four 
irons consist essentially of a-nickel-iron (kamacite), with minor 
amounts of y-nickel-iron (taenite). Associated with the iron are 
minor amounts of various iron-nickel phosphides. In the nodules 
are found other phosphides together with graphite, pyrrhotite 
and troilite. 
The oxidized crust or scale of the meteorites consists chiefly 
of limonite, with residual patches of nickel-iron metal and some 
of the phosphides, chiefly rhabdite. In places, trevorite is 
associated with it, and some of the scale exudes or is encrusted 
with small quantities of the chlorides of iron and nickel. 
Nickel-iron Alloys 
The a-nickel-iron (kamacite) is iron white and isotropic, 
strongly magnetic and readily scratched with a needle. The 
standard etching reagents affect it as follows : nitric acid 
produces an immediate etching, but without effervescence ; 
hydrochloric acid fumes tarnish, and the iron washes and rubs 
brown, but the effect is not consistent; potassium hydroxide and 
potassium cyanide are negative; ferric chloride instantly turns 
the iron brown, bringing up grain boundaries and etching grains 
differentially, as well as bringing up Neumann lines; mercuric 
chloride darkens the surface immediately. Picric acid (2 per 
cent, in alcohol) and bromine water darken the kamacite and 
bring up grain boundaries and crystal structures. 
The y-nickel-iron (taenite) occurs only as occasional groups 
of parallel lamellae interleaved with the kamacite plates, and as 
small triangular areas in the interstices of the kamacite grains. 
It can scarcely be distinguished from the kamacite in unetched 
sections, but is readily distinguished after etching with picric 
acid, bromine water, or 2 per cent, nitric acid in alcohol, all of 
which darken the kamacite but do not affect the taenite. Of the 
standard etching reagents, nitric and hydrochloric acids, potas- 
sium hydroxide, ferric chloride and mercuric chloride give 
negative results. Hydrochloric acid fumes tarnish the taenite 
brown, but the results are not consistent. The taenite is isotropic, 
strongly magnetic, and is readily scratched with a needle. 
The factors controlling the disposition of the taenite lamellae 
in the kamacite have been discussed elsewhere (Edwards and 
Hodge Smith, 1941). 
