Carborundum does occur in naturally in meteorites, as the mineral moissanite, but it is very rare, and crystals are almost always tiny or microscopic.
Carborundum is a man made silicon carbide which is manufactured most often for abrasive products. Think sandpapers and grits.
Is it pretty? Yes! The rainbows of color are mighty attractive. But beware! Its edges are sharp and it is quite fragile. Little pieces will fall everywhere if it is mishandled (or handled at all actually).