Vicanite-(Ce)

vicanite-(Ce)

asbecasite

hellandite

stillwellite-(Ce)

Images

Formula: (Ca,Ce,La,Th)₁₅As⁵⁺(As³⁺,Na)_0.5Fe³⁺_0.7Si₆B₄ (O,F)₄₇
Nesosilicate (insular SiO₄ groups), vicanite group, cerium-, lanthanum-, thorium- and arsenic- bearing mineral
Specific gravity: 4.73 calculated
Hardness: 5 to 6
Streak: White
Colour: Green, yellow
Environments

Volcanic igneous environments

Localities

At the type locality, Tre Croci, Vetralla, Viterbo Province, Lazio, Italy, vicanite-(Ce) occurs as rare transparent yellowish green anhedral grains, up to 0.3 mm in size, in small myarolitic cavities inside an ejectum of syenitic composition. The host rock shows a hornfels-like texture in thin section, and the main constituents are K-feldspar (high sanidine), plagioclase, clinopyroxene, monoclinic amphiboles and magnetite. Small crystals of biotite are often present as inclusions in the amphiboles. Accessory phases include apatite, titanite, antimony-bearing asbecasite, thorium-bearing hellandite, thorite, zircon, thorian uraninite and stillwellite-(Ce). Most of the accessory phases appear to have crystallised later than the host rock, except for vicanite-(Ce) and thorium-bearing hellandite which are occasionally found enclosed in the K-feldspar mass (EJM 7.439-446).

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