This one lies on a hillside near Glendrian Caves on the north coast of Ardnamurchan. It's unusual in that, unlike many of them, the source of this particular erratic is relatively easy to identify.
A thin-section of a garnet-mica schist is seen in this video from Geosec Slides, a West Ardnamurchan business.
Garnet-mica schists are common in the Moine Schists, a formation of rock which is found to the immediate east of West Ardnamurchan, so this rock must have travelled at least ten kilometres.
Many thanks to Rob Gill for showing The Diary the erratic. Rob's website is here.