The auctioneer Bonhams says the carved granite step is a Sandakada Pahana - or moonstone - similar to those found in temples dating from Sri Lanka's Anuradhapura period (c400BC-1000AD).
After a brief stint as a salesman at Bulgari in New York he returned to Paris in 1977 and started designing pieces that relied at first on inexpensive stones like coral, moonstone and minute colored diamonds.