Prisma Gabbro Obelisk
Gabbro is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface.
Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism. By rough analogy, gabbro is to basalt as granite is to rhyolite.
These superb patterned and grained specimen came from central Madagascar. The polishing work is made by local people.