metamorphosed limestone

Derives from the Greek "μάρμαρον" (mármaron), from "μάρμαρος" (mármaros), "crystalline rock", "shining stone", perhaps from the verb "μαρμαίρω" (marmaírō), "to flash, sparkle, gleam". This stem is also the basis for the English word marmoreal.

... or it would be if it was marble, but sadly it's just an imitation - cheap plastic laminate affixed to hardboard to create a decorative backing within my fireplace surround.