Fragment of Roman "Graphic" black Porphyry Marble Silver Pendant

An extremely rare fragment of real "graphic" black Roman porphyry has been set in this sterling silver pendant. This marble has white tending to green or light green incusions, the arrangement of which suggests the image of a handwriting, hence its name. Its quarries were the same as those of red porphyry; it was used in the 1st and 2nd century AD. : we have a slab of this marble visible in Rome in the Church of San Saba, walled up in the right aisle