' A very well-known fact on the diamond-fields, and one rather in favour of the euphotide (?) being the mother rock, is
that each of the pipes furnishes diamonds easily distinguishable from
those found in the others. Bulfontein produces small white stones,
occasionally specked and flawed, but very rarely coloured; while Du
Toits Pan, within half a mile, seldom yields other than coloured
stones. So well marked are the characteristics of the diamonds from the
various diggings, that diamond buyers can generally tell by the
appearance of a stone the locality from which it has come.'
Mr.
Dunn's paper was followed in the same year by a description of the
microscopic character of the diamond-bearing rock by Professor N. S.
Maskelyne and Dr. W. Flight.1
The
specimens examined and analysed by them were unfortunately all
decomposed more or less, none coming from a depth greater than 180
feet. They identify a bronzite (two varieties, one bright green, one
buff coloured), a variety of smaragdite, garnet, ilmenite, a diallage
(much altered) and a mica-like mineral. Opaline silica, occasionally
hyalite, sometimes resembling hornstone, is disseminated through the
rock ; the mica-like mineral is described, analysed, and named vaalite,
it being regarded as an outlying member of the vermiculite family; the
smaragdite, in brilliant greyish green fragments, green bronzite and a
much altered bronzite, resembling that in the meteorite of Breitenbach,
are also analysed, as is the rock of Bultfontein. This gives (water
being undetermined) :—
