With the J urassic beds is associated an extensive series of eruptive rocks (gabbro, peridotite, serpentine, diorite, granite, &c.); they are chiefly of Jurassic age, but the eruptions may have continued into the Lower Cretaceous.
Tremolite-schist and anthophyllite-schist are in nearly all cases the representatives of the ultra-basic igneous rocks such as peridotite in regions of high metamorphism.
The main mineral deposits are the nickel ores, occurring as veins of garnierite, associated with peridotite dikes, in the ancient rocks of the eastern slope of the island.
It appears to consist chiefly of gabbro, peridotite, serpentine and other very basic eruptive rocks, which are believed to be of Cretaceous age.
In 1906 a number of small diamonds were discovered in an altered peridotite somewhat resembling the S.
In 1906 diamonds were found in a peridotite dike in Pike county 22 m.
In the Rajmahal Hills basaltic lava flows are interbedded with the Gondwana deposits, and in the Karharbari coalfield the Gondwana beds are traversed by dikes of mica-peridotite and basalt, which are supposed to be of the same age as the Rajmahal lavas.
Peridotite and gabbro form much of the eastern peninsula (Banggai).