THE MATRIX OF THE DIAMOND 57
discussion
as Kimberlitc, as to whether they are tuffs or lavas. Haidinger was one
of the first to describe the so-called meteorite-breccias, and to show
that not only are angular fragments of other rocks frequently enclosed
in the olivine rock, but that the meteoric rock itself is often broken
into angular and rounded fragments cemented together, as if a volcanic
tuff. Tschermak' holds to the tuff-like character of certain
meteorites, yet remarks that— ' There occur passages into the tuff
structure, so that the same stone may be designated by one observer as
crystalline, by another as clastic' Another structure in these olivine
meteorites is the occurrence of rounded masses of olivine or of olivine
and enstatite, called the chondritic structure. The origin of this has
given rise to much discussion. A chondrus may consist of a single
optically continuous mass of olivine, or it may be polysomatic, that
is, due to a number of individuals.
Polysomatic
chondri of olivine occur in the Kentucky Kimberlite. The olivines are
laid together, as if in a mosaic, the whole forming an irregular
sphere. This is identical with a granular chondrus in a meteorite from
Seres figured by Tschermak.2 Glass which occurs in these chondri occurs also in a chondrus from Kimberley.
1 Die mikrosk. Bcschaff. der Meteoriten, Stuttgart, 1885, p. 3.
2 Ibid. (Plate VIII. fig. 2.)
