A Whitby jet necklace, the facetted oval and round beads knotted on black thread, total length 1200 mm., Whitby jet is a natural organic gemstone formed from the compressed wood of the monkey puzzle or araucaria tree, found along a two mile stretch of coastline between Robin Hood's bay and Boulby, nearby to Whitby, north Yorkshire. Whitby jet gemstone is formed over 186 million years ago.