Late‐stage beryllium silicates from the Sels‐Vitberget granitic pegmatite, Kramfors, central Sweden

Abstract

The beryllium silicates bertrandite, euclase, and phenakite have been identified replacing primary beryl in a small alteration zone in the upper part of the Sels‐Vitberget pegmatite. Within a few square metres of outcrop, beryl crystals intergrown with microcline perthite are more or less completely altered to a coarsely crystalline and drusy mixture of Be silicates and quartz. Some seriate and minor apatite also occur in this association. The beryl pseudomorphs exhibit a diffuse zoning, with the core portion dominated by the most common Be silicate, bertrandite. Euclase occurs in lesser amounts, often intergrown with bertrandite. Phenakite is more rare and generally confined to finer‐grained drusy border rims of the former beryl crystals; the texture indicates that phenakite is not in equilibrium with bertrandite + euclase (+ quartz). The formation of Be silicates at Sels‐Vitberget is apparently related to the percolation of gradually evolving, late‐stage, acid to neutral fluids on a local scale in the pegmatite. This took place at low to moderate pressures (below greenschist‐facies conditions) and temperatures in the range 200–300°C.

Jonsson, E. & Langhof, J., 1997: Late‐stage beryllium silicates from the Sels‐Vitberget granitic pegmatite, Kramfors, central Sweden. GFF, Vol. 119 (Pt. 3, September), pp. 249–251. Stockholm. ISSN 1103–5897.

Keywords:

• Bertrandite
• beryl
• euclase
• phenakite
• granitic pegmatite
• late‐stage alteration
• Sweden