Bannisterite is an extremely complex manganese iron calcium potassium sodium aluminosilicate originally described in 1968 from Co-Type Localities: Benallt mine in Gwynedd, Wales and Franklin mine in New Jersey, USA. At Benallt mine material was identified earlier as something new by Frederick Allen Bannister who was at the time a researcher at the Natural History Museum in London, but there was not enough pure material for a full description to be published. Later, it was realized that the same substance occurred at Franklin mine, but had been mis-identified. The combined efforts led to its formal naming and publication in honour of Bannister. Ironically, at around the same time, amazing large crystals of Bannisterite were being recovered from Broken Hill mine in Australia, but were also mis-identified. These ferroan Bannisterites are without question the finest examples of this extremely rare species. This large miniature specimen is pure ferroan Bannisterite with foliated micaceous crystals to a staggering 6 cm across. It comes from the superb systematic collection assembled by the brothers Martin and Michael Günther (1951-2007 & 1956-2021).
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