Cancrinite: Gemstone Information
A semi-opaque yellow-coloured fibrous variety of cancrinite,Na6Ca2Al6Si6O24(CO3)2, has been cut into beads and cabochons. Cancrinite is occasionally found as crystals of the hexagonal system; the RI approximate to 1.50, which is all that would be expected to be seen from the massive gemmy material. The crystals of cancrinite have RI for the ordinary ray of 1.515–1.524 and for the extraordinary ray of 1.491–1.502, the DR of 0.022, uniaxial negative. The SG varies from 2.42 to 2.50 (a specimen of Canadian gem material gave a value of 2.435).
The hardness is 5–6.Yellow gem cancrinite does not luminesce under UV but an orange-yellow response has been observed under X-rays. Cancrinite effervesces with acids. While cancrinite is found in several places, gem-quality material usually originates from Bancroft and French River, Ontario,Canada. Cancrinite is found in pegmatites in nepheline syenites. Othercolours, including light greyish purple, yellow, violet and orange have come from Canadian sources and a blue variety from Greenland, this material being reported to show dark violet under LWUV and dark red to purple under SW.