These links will produce listings of pitchstones from the online catalogue of the Hunterian Museum and Art Gallery. Torben Bjarke Ballin and I have been working to produce a gazetteer of Arran pitchstone localities (now published online at: http://www.sair.org.uk/sair38/) to help constrain lithic studies of archaeological pitchstone artefacts. As a by-product, I have been looking at pitchstones in our geological collections, and improving their curation, and transferring data to the computer catalogue. These records are now available online.
The catalogue database contains almost all our holdings of pitchstone specimens from Arran, plus an incomplete, but representative selection of pitchstones from other Scottish localities. It also contains a limited selection of felsites which are associated with pitchstone, especially from Arran. There are images of almost all hand-specimens, plus photomicrographs of specimens which have been sectioned.
You can find pitchstones that match your own criteria using the huntsearch online catalogue.
Try searches such as:
pitchstone and brown and arran
or
pitchstone and porphyritic and fayalite
Comments welcome - email J.Faithfull@museum.gla.ac.uk