THE MATRIX OF THE DIAMOND 43
The
larger diamonds from Kimberley have been the subject of study by
several investigators. They have been found sometimes to have optical
anomalies due to strain, so that they are not perfectly isotropic,
Fizeau thought this strain to have been caused by the unequal
distribution of heat during rapid cooling ; but Jannettaz' holds that
the strain is due to compressed gas in the interior of the crystal. The
latter theory seems to be supported by the fact that the diamonds
frequently crack or fly to pieces after having been taken from the
mine. It is a phenomenon perhaps similar to that which occurs with the
smoky quartz of Branchville, Connecticut, which, as Wright'2 has proved, is filled with liquid carbonic acid, and flies to pieces with a report when struck, as so well described by Hawes.3
The fact that fragments of the diamonds are often found separated in
the mine has been used as an argument that the blue ground is not a
volcanic rock but an aqueous mud derived from one. This argument falls
to the ground on our knowing that the separation of these fragments is
not due to a flow of the matrix, but to the bursting of the diamonds
themselves on exposure to the atmosphere.
The Kimberley diamonds contain various enclosures,4 among which hematite is the most abundant. Zirkel,' before the discovery of the South African diamond mines, gave a full resume of the inclusions in diamonds. Schrauf6 has described a curious case of one diamond enclosed in another, a fact formerly mentioned by Kenngott.7 The researches of Harting8 upon inclusions in diamonds, as
