frequent
occurrence, but in some cases of greater interest from the point of
view of the origin of the Diamond, are Diallage, Tremolite,
"Wollastonite, Ilmenite, Magnetite, Chromite, Zircon, Sapphire, Topaz,
Tourmaline, and Rutile.
Other
minerals of more recent secondary origin, as Calcite and some of the
Zeolites, are found, but they are of much less importance in the
present respect. The Diamonds themselves occur either in crystals or
in broken fragments, often in cleavage octahedra.
India
for long furnished the whole output of Diamonds, but to-day the case is
very different. Still, the localities where the mineral has occurred
are numerous, and have furnished some of the most interesting data for
consideration with regard to the origin of the gem. When the Diamond
was first found in India is not known, but Ptolemy refers to its
occurrence there.
The
famous Golconda mines are really far from the place of that name, being
situated in various groups, distant 100 to 200 miles to the south and
east of Golconda. The most southern of these mines are along the Penner
river, and to the south of Karnul, and between it and the Penner is
another series. To the north-east again, on the Kistna river, are the
mines of Kollur, whence are supposed to have come the Koh-i-Noor, the
blue "Hope" Diamond, and the Great Mogul. In all these mines the
mineral occurs in some derived rock, sometimes in a loose sand, as at
Kollur and Partial, or in alluvium, as at the Chennur mines. At the
mines to the south of Karnul the Diamond occurs in a bed of
conglomerate of fragments derived from shales and Lydian-stone, only a
few inches thick. At Muleli, between the rivers Kistna and Godavari,
the rock containing the
