A Contribution to the Study of the Diamond Made. 
165 
repeated and constant Experience, and as a known thing in their Art, that 
'twas almost impossible (though not to break, yet) to split Diamonds, or 
cleave them smoothly cross the Grain (if I may so speak) but not very 
difficult to do it at one stroke with a Steeled Tool, when once they had 
found out from what part of the Stone, and towards what part the splitting 
Instrument was to be impell'd : By which 'tis evident that Diamonds them- 
selves have a grain, or a flaky Contexture not unlike the fissility, as the 
Schools call it, in Wood" (*An Essay about the Origine and Virtues of 
•Gems,' 1672, p. 21). 
If the grain of a diamond, as revealed either by a fracture at right angles 
to an edge of the octahedron or by the natural face of the dodecahedron, 
represents lines of crystal growth (as seems not unreasonable as a first 
assumption), then it follows that the proximate primitive form of diamond 
is not an octahedron but a six-rayed figure defining cubical space — each ray 
joining the mid points of pairs of opposite edges of the cube and delineating 
tlie respective directions of accretion. Thus let AG-, Eig. 7, be a cubical ray 
space (or space lattice), a, h, c, d . . . , the mid points of the respec- 
tive edges. Then am, hn, cJc, dl, eg,fh, are the directions of the rays. The 
crystallisation may be supposed to proceed by successive symmetrical 
impositions, edge to edge, of , like cubical spaces containing the rays, each 
cubical ray space being surrounded by twelve others, that is, a second ray 
space A' G' will be applied to AG in such a way that E' E' lies along DC, 
a third A" G" so that A" B" lies along HG, and so on. The overall outline 
of the first 13 ray-spaces will define a cubical space equal to 27 primitive 
cubes of which 14 are empty. The addition now of a ray space opposite 
each face of the central one gives an octahedron of 17 ray spaces. If, 
further, we may venture to regard a, b, c, d . . . , each as indicating 
the place of a carbon particle, then each particle in a diamond crystal will be 
surrounded symmetrically by six others b, n . . . , at equal distances p 
(where _p is the length of an edge of the cube), in directions db, dn . . ., 
parallel to the edges of the cube ; by eight others a, c, h, e . . . , at 
equal distances ^/t/ 2, in directions da, de, dh, de, . . . , parallel to the 
edges of the octahedron ; by twelve others, R, S, . . . , at equal 
distances v/3 p in directions c?E, dS, dT', dJJ' . . . (where c^R, cZS pass 
through P and Q the middle points of the cubic faces AE, DG ; and dT\ 
dV, are parallel to BQ, BP) parallel to the edges of the rhombic dode- 
cahedron. In short dn ( = p), dl (= \/2p),^ cZS (=\/ 3^), delineate in 
magnitude and direction one edge of a cubical, octahedral, and dodecahedral 
space respectively. Again each particle in the crystal of this proximate 
structure is surrounded by 32 others, the whole forming a system of 33 
contiguous particles. An interesting feature of the configuration is the 
* dl = 2 da = 2 (p/n/2). 
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