Chariots on Fire introduces: 

Boulder Opal

Amongst the rarest varieties of opal, Boulder-Opal embeds itself on the surface of sedimentary rock—sandstone or ironstone, customarily—which lends it a unique durability. A stone endlessly reticent of any singular tonal expression, it displays an unpredictable, seemingly mystic diffraction of light—the literal manifestation of ‘opalescence.’ Ancient Greek mythology spoke of the opal as ‘Zeus’s tears;’ Arabic legend claims the stone to be born at the moment of a lightning rod’s strike to the earth. In equal manner does the Boulder-Opal harness for itself the seeming dichotomies of fire and ice—across the stone’s interplay of color, each surges forth to a kind of mesmerizing coexistence.