{"product_id":"stilbite-ca-on-calcite","title":"STILBITE-(Ca) on CALCITE","description":"Helgustadir mine on the east coast of Iceland is the world-famous source of optical grade double-refractive Calcite, known as 'Iceland Spar'. It's optical properties have been known since 1669, but official mining began in 1855 and ended in 1925. Since 1975 the site has been a national monument with collecting strictly forbidden. This lovely large miniature specimen was collected pre-1975 and has been in David Hardman's fine collection of worldwide zeolites since then. It consists of a well-formed rounded rhombic crystal of Calcite, 4.6 cm across, with natural etched faces (so no double-refraction visible), but one side it covered in perfect, cream coloured, flat, bladed Stilbite crystals. The Stilbite crystals are in great condition and reach nearly 1 cm in length. Zeolites from Helgustadir mine are now so rarely seen for sale, just the occasional quality specimen in older collections that become available.","brand":"Crystal Classics","offers":[{"title":"Default Title","offer_id":46549944008879,"sku":"CC49630","price":500.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0710\/8516\/2671\/files\/CC49630.png?v=1770653257","url":"https:\/\/crystalclassics.com\/products\/stilbite-ca-on-calcite","provider":"Crystal Classics","version":"1.0","type":"link"}