Galena and sphalerite. Shullsburg, Wisconsin, USA

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Sphalerite (light grey) occurs as radiating aggregates of different grain sizes. Very fine-grained sphalerite is poorly polished and shows reddish-brown or light-coloured internal reflections (top and bottom right). The central bands of sphalerite have grown into a vug and hence have euhedral crystal terminations. Galena (white) has infilled most of this central vug. Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

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