Gabbro (Eucrite), Ardnamurchan.

This is a thin section microscope slide of Eucrite from the tertiary volcanic centre in Ardnamurchan, on the West Coast of Scotland. Famous for its complete ring dyke made of this material (or is it a Lopolith?). It is a gabbro consisting mainly of plagioclase feldspar, classic albite twinning, with large olivine crystals and pyroxene. Very interesting partial alteration of the olivine, mostly brown iddingsite developing along the characteristic olivine cracks, but at the edge the alteration has progressed further and magnetite has formed. Where this has happened the surrounding olivine has been altered to a fine crystalline mineral, (yet to be identified, possibly talc). Good clear slide, shows the minerals well.
1 Slide

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