The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Yellow scapolite’s value depends on size, clarity, and strength of color. Expect the usual premiums on price in terms of color saturation and custom versus native or commercial cutting. Values for natural purple or violet scapolites differ greatly from irradiated stones, since the untreated stones are rarer and have a delicate, but much purer, purple.
Prices for untreated purple stones would exceed yellow, while prices for irradiated purple stones fall below yellow.
Rare cat’s eye scapolites are highly varied and quite beautiful.
Tanzanian golden scapolite is much darker in tone than the Brazilian material, as well as much cleaner. Moreover, there is enough available to make jewelry promotion feasible.