in Natural History, the name of a genus of spars. The word is derived from the Greek ἀνομοί, irregular, and ρόμβος, a rhomboidal figure. The bodies of this genus are pellucid, crystalline spars, of no determinate or regular external form, but always breaking into regularly rhomboidal masses; easily fissile, and composed of plates running both horizontally and perpendicularly through the masses, but cleaving more readily and evenly in a horizontal than in a perpendicular direction, the plates being ever composed of irregular arrangements of rhomboidal concretions.