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The Mines and Minerals of Lavrion - Andersonite

Last Updated: 21st Mar 2020

By Branko Rieck

ANDERSONITE, Na2Ca(UO2)(CO3)3 · 6H2O, trigonal

General Appearance
Mostly andersonite forms crystalline crusts in fissures perpendicular to the surface of the gypsum cavity in which it appears. Slickenside structures have been observed (see Figure 1). In rare cases andersonite forms tiny rhombohedral, pseudocubic or flattened crystals. The small size, combined with the light color makes it near impossible to make the shape out in daylight (Figure 2), but if illuminated with either shortwave or longwave ultraviolet (UV) light, the outlines of the crystals are clearly visible (Figure 3). Andersonite is yellow-green to bright yellow: As a rule of thumb it can be stated that the smaller the grain size, the less pronounced the green hue becomes. The fine-grained slickenside is bright yellow with no perceptible green component. In UV light it shows a very strong reaction with a blue-green tint (Figure 3).

Andersonite is part of the uranium-bearing paragenesis from the Paliokamariza Mine No. 18. There, it is an important indicator for the uranium-bearing minerals because of its strong UV fluorescence.

A detailed history and description of the only locality for andersonite is given in the article ”The Mines and Minerals of Lavrion - Uranium minerals from Paliokamariza Mine No. 18”.

Fig. 1: Yellow andersonite slickenside on gypsum. This photo by Dr. Harald Schillhammer was first published in Rieck, B., Kolitsch, U., Voudouris, P., Giester, G. and Tzeferis, P. (2018): Weitere Neufunde aus Lavrion, Griechenland. Mineralien-Welt 29 (5), 32-77 (in German). FOV: 15 mm.

Fig. 2: Tiny yellow andersonite crystals on white gypsum. Inclusions of andersonite color the gypsum yellow-green in some places. FOV: 2.5 mm.

Fig. 3: The same view as figure 2. This photo was made under 365 nm UV light.

Thanks go to Dr. Uwe Kolitsch for constructive comments and diligent proofreading to improve this article.

Rieck, B., Kolitsch, U., Voudouris, P., Giester, G. and Tzeferis, P. (2018): Weitere Neufunde aus Lavrion, Griechenland. Mineralien-Welt 29 (5), 32-77 (in German).

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