CANCRINITE: Bigwood Township, Ontario, Canada (~3 inches across). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Cancrinite is one of the most attractive of all opaque or translucent gem materials. It is a bit too soft for average wear, but its distinctive color is worthy of jewelry. Cancrinite may be tricky to cut because it often contains numerous hard inclusions. Faceted gems even as small as 1 carat are considered great rarities.
| Data | Value |
|---|---|
| Name | Cancrinite |
| Colors | Colorless, white, yellow, orange, pink, to reddish, pale blue, bluish gray. |
| Crystallography | Hexagonal. Crystals prismatic, but rare; usually massive. |
| Refractive Index | 1.488-1.528 |
| Luster | Vitreous; pearly on cleavage; greasy |
| Hardness | 5 - 6 |
| Fracture | Uneven |
| Specific Gravity | 2.42-2.51; Vishnevite: 2.3. |
| Birefringence | 0.022 (cancrinite); 0.002-0.012 (vishnevite). |
| Cleavage | Perfect 1 direction |
| Dispersion | Weak |
| Stone Sizes | Masses occur up to several pounds, but Cancrinite is usually in veins a few inches across. It is usually cut as cabochons and beads. The Canadian material is orangy yellow in color, with a greasy luster. Faceted stones are exceedingly rare and always less than 1-2 carats. |
| Luminescence | None in UV. X-ray orange-yellow. |
| Luminescence Present | Yes |
| Luminescence Type | X-ray Colors |
| Transparency | Translucent to opaque. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
(Na,K, Ca)6-8(Al, Si)12O24(CO3,SO4,Cl)1-2 · nH2O. |
| Optics |
o = 1.507-1.528; e = 1.495 -1.503 (cancrinite). o = 1.490-1.507; e = 1.488 -1.495 (vishnevite). Uniaxial (-), chlorine-rich variety (microsommite) is optically (+) |
| Optic Sign | Uniaxial +, Uniaxial - |
OPTICS:
o = 1.507-1.528; e = 1.495 -1.503 (cancrinite)
o = 1.490-1.507; e = 1.488 -1.495 (vishnevite)
Uniaxial (-), chlorine-rich variety (microsommite) is optically (+)
OCCURRENCE: Primarily in alkali-rich rocks; also as an alternation product of nepheline.
Iron Hill, Colorado; Kennebec County, Maine
Norway; Romania; Finland; Russia; North Korea; China; Democratic Republic of the Congo; India; Uganda; Kenya.
Bancroft District, Ontario, Canada: fine gemmy material.
COMMENTS: Cancrinite is one of the most attractive of all opaque or translucent gem materials. It is a bit too soft for average wear, but its distinctive color is worthy of jewelry. Cancrinite may be tricky to cut because it often contains numerous hard inclusions. Faceted gems even as small as 1 carat are considered great rarities.
NAME: After Count Cancrin, Finance Minister of Russia.
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