Have a look at some of the excellent thin section images in this collection (called the Heddle Collection) in the Hunterian Museum, University of Glasgow:
There are dolerites (called syenites in the old days) -- similar to the spotted dolerites that we all know and love from the bluestone circle at Stonehenge -- as well as samples from the sarsens, and two different rock types, both labelled as "Altar Stone" samples. I have put up a post about this before:
The Hunterian info is here:
Last time I looked, there was a slide of the Altar Stone sandstone, numbered C3. Now, however, the slide seems to have disappeared. It's not on the photo of the slide tray, and on the descriptions of the slides the sample is mentioned, but again the image of the sandstone has disappeared.
Strange goings-on in Glasgow. Is there some censorship going on here? Not only do we have the mystery of the "volcanic breccia" being labelled as "Altar Stone" -- but now we have an Altar Stone sandstone sample that has been removed from public view. Why? Answers on a post-card please.....