Pickeringite from Fåvang
1, 2, 3, 4

Some years ago a fibrous mineral was found near the Host sæter at Fåvang in Gudbrandsdalen. The Finder, Mr. Fröisland, sent a sample to the Norwegian Geological Survey for determination. The mineral has a conspicuous silky lustre. In some parts of the specimen the fibres are nearly white, with a faint yellowish tinge only; in other parts they are yellow. Some parts of the specimen are reddish brown, this colour evidently originating from ferric hydroxide. The mineral is easily dissolved in water and has a bitter (astringent ) taste. Qualitative chemical tests proved that it is rich in water. Further, A12O8 (with a very small amount of Fe2O8), MgO and SO4 were easily assigned. CaO and Cl are absent. A determination of the alcalies was carried out by Mr. Emil Klüver, showing Na2O 0.29%, K2O 0.07%. (According to Mr. Klüver the last figure may be too high. It is possible that only traces of K2O are present, the portion available for the analysis being 0,4 g only).

Microscopic examination of the pulverized material proved that the bulk of the specimen consists of an extremely fine fibrous mineral - the macroscopic fibres are composed of numerous subparallel microscopic ones, with = 1.473 and = 1.484. (On account of the fineness of the fibres, the measurements are probably not very accurate. The error may be 0.003 ±). The elongation is positive, the angle of extinction ca. 35° (measured on fibres with maximum interference colour ). The fibrous mineral is consequently pickeringite MgO · Al2O3 • 4 SO8 • 22 H2O.