An agate and cultured pearl necklace, Jean Vendome, French. photo courtesy Bonhams

centering a dendritic agate rectangular panel bordered by baroque freshwater cultured pearls, suspended from a detachable necklace of fifty-six drop-shaped freshwater cultured pearls; with French assay mark and maker's mark; mounted in eighteen karat gold; necklace length: 14in. Estimate: $700 - 900

Bonhams. The Collection of Laura Speiser, featuring jewelry by Andrew Grima, 19 Oct 2010. New York, Los Angeles and San Francisco www.bonhams.com