Kentish Rag is definitely local. Dolerite I think is fairly generally used in geology, but I see from wikipedia that N America has its own usage of diabase. The diabase article is interesting. The Whin Sill in the north of England is a basaltic intrusion that cooled more quickly than the deeper rocks which would form gabbro, so has smaller crystals, visible with a handlens, where extruded basalt has a far finer texture, as you say. The crystals would be smaller than in granite, and the chemistry, as you imply, the same as basalt. As the word whin refers to a plant, I think the name has moved to rock from the flora growing on the outcrop of the sill. (The sill is interesting because it formed the natural boundary used by the Romans for Hadrian's Wall, and also the islands of Lindisfarne and Holy Island.)
I took some more books into Oxfam, and bought a couple of unstrung bead necklaces which I have restrung with some of my own stock of beads. I'm not sure whether to keep them as gifts for people, or take them back as a donation for Oxfam again. I also attempted to restring and old necklace I got from my mother years ago. It has triangular beads with two holes which form an overlapping snakelike pattern, but I got the threading of the ends wrong where I added some beads to make the length better. I need some thread I think, rather than the wire I usually use, as it wasn't flexible enough.