344 Derivation of the Diamond from Anthracite. 
the other, that the majority of diamonds, when burned, leave 
a slight ash. 
I have no wish, however, to affirm that anthracite is the 
only body which can crystallise into the diamond. On the 
other hand, I think we have been too ready to assert that 
all diamonds must have been produced in the same way. 
This does not seem probable. Many substances can be erys- 
tallised in six different ways, viz., by melting, by dissolving, 
or vaporising them, by decomposing their gaseous or liquid 
compounds, and by inducing crystallisation in them whilst 
they are solid. Carbon may crystallise in most, perhaps in 
all of those ways, and the genesis of one diamond be quite 
different from that of another. 
I would only further remark, that the question, whether 
earbon will crystallise as graphite, or as diamond, will mainly 
be determined by the rapidity with which crystallisation is 
effected, and the temperature at which it occurs. 
Graphite certainly represents the most stable equilibrium 
of the crystalline molecules of carbon at a high temperature ; 
for melted cast-iron, containing excess of carbon, separates 
the latter as graphite when it solidifies; and the diamond, if 
suddenly raised to a white heat, changes into the same sub- 
stance ; but at lower temperatures the diamond must be re- 
garded as exhibiting the more stable molecular equilibrium. 
In truth, a crystal like the diamond, belonging to the tes- 
sular system, with its three equal crystallographic axes, and 
its inability to refract doubly or polarise light, appears the 
most complete expression of crystalline molecular equili- 
brium. Whenever, therefore, carbon crystallises very slowly, 
and at moderate temperatures, it may be expected to become 
the diamond ; and graphite, when not maintained at a high 
temperature, must be looked upon as a substance whose par- 
ticles are ‘in a state of unstable equilibrium, and as con stantly 
tending, therefore, to have this equilibrium overturned so as 
to attain that which characterises the diamond. ; 
50 
Lili 
T R 0 
