Silver Whitby Jet Marcasite Butterfly Brooch. M326. This stunning butterfly brooch is handmade in sterling silver and features four beautifully hand carved marquise shaped Whitby Jet gemstones, sourced directly from the north east coast of Yorkshire, which are surrounded in a silver frame accented with sparkling Marcasite gemstones. It is an exquisite and detailed piece which would make a beautiful gift. All our Whitby Jet jewellery is designed and crafted within our very own workshops in Derbyshire where a team of skilled craftsmen turn the raw Jet into these stunning pieces of jewellery. You can find other matching Whitby Jet jewellery on our website. Silver Whitby Jet Marcasite Butterfly Brooch. 24x34mm.