Banalsite

banalsite

tephroite

alleghanyite

Images

Formula: Na₂BaAl₄Si₄O₁₆
Tectosilicate (framework silicate), feldspar group, forms a series with stronalsite
Specific gravity: 3.05 calculated
Hardness: 6
Streak: White
Colour: White
Solubility: Decomposed by hydrochloric acid
Common impurities: Mn,Mg,Ca,K
Environments

Metamorphic environments
Hydrothermal environments

Banalsite is a rare mineral which was the first barium aluminium silicate to be described with sodium as the dominant alkali; it forms under hydrothermal or metamorphic conditions (MW).

Localities

At the type locality, the Benallt Mine, Rhiw, Aberdaron, Gwynedd, Wales, UK, banalsite is found in veins and vugs where it is associated with a suite of minerals believed to have been derived from hydrothermal activity involving manganese-rich fluids exhaled onto the Ordovician sea floor. The banalsite typically forms thin bands of coarsely crystalline material cutting dark spotted manganese ore, and crystals of banalsite to 2 mm have been found in small cavities in the ore body. In all occurrences in the mine banalsite is associated with calcite, baryte, tephroite, alleghanyite, jacobsite, biotite, natrolite and harmotome (AM 30.85, MW, Mindat, HOM).

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