320 Journal of the Asiatic Society of Bengal. [September, 1912. 
tion of pressure would lead to a reaction between the outer 
shell of the diamond and the surrounding iron with an increase 
of 2-7 % in volume calculated on the constituents that partici- 
pated in the change. With a further decrease in pressure the 
carbide would itself break down into metallic iron and graphite 
with a 5:1 °% increase of volume, whilst the remaining diamond 
would pass into graphite with a 57°8°, increase of volume. 
From the Cafion Diablo meteorite we obtain, therefore, indica- 
tions of a small release in pressure, promoting the formation 
round the diamond of a carbide zone analogous to the kelyphite 
rim round garnets in certain eclogites. In certain siderites the 
of diamond into graphite, as in Moissan’s experiments on the 
artificial production of diamond. 
Cliftonite, discovered by Fletcher in the Youndegin iron, 
piteieice regarded as a third modification of 
cite (Fe,, Ni) 
Another explanation would be that the diamond-bearing siderites 
represented those parts of the metallic core of the primitive body that 
2 . Mag., VII, pp. 126-130 (1887). 
® Cohen, Meteoriten Kunde, I, pp. 140-1. 
