Thank you for submitting your item for appraisal. This appears to be a saltwater cultured pearl necklace , 6.0-6.5 mm, very good lustre and complexion, clasp with one approx 3.0 mm cultured pearl, stamped "750" and with Mikimoto hallmark (?), 20 inches long. The estimate is based on similar necklaces sold at auction. "Asking prices" in the trade can be much higher, retail prices are approx. 2500 USD for similar size and quality. The mass production of chinese sweatwater pearl necklaces have put pressure on the value of pearl necklaces in general.