Pyrite, jamesonite, sphalerite and galena. Ireland

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Pyrite (pale yellow) is rhythmically banded with the growth bands picked out by very fine gangue inclusions. Pyrite has nucleated on sphalerite (light grey, top right) and on galena (blue-white, bottom left). Pyrite has been fractured and recemented by calcite (dark grey, bottom left), which shows multiple twinning (top centre) and faint light internal reflections. A blue-white acicular to tabular sulphosalt (centre) has a similar reflectance to galena, but is better polished and is highly anisotropic; it has the optical properties of jamesonite.

Polished block, plane polarized light, x 110, air

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