From Longman Dictionary of Contemporary Englishmoonstonemoon‧stone /ˈmuːnstəʊn $ -stoʊn/ noun [countable, uncountable] DCJa milky-white stone used in making jewellery a moonstone necklace
Examples from the Corpus
moonstone• It depicts an angel with enveloping wings sitting in a boat; shining above them is a moonstone.• Then on the fifth day, mid-morning, a pool of light as pale and clear as moonstone appeared on the horizon. 