Ronald, in London the museum to go for is The Geological Museum,
located in South Kensington. This is the main “museum area” in
London, it also has The Science Museum and the Victoria and Albert
(usually called the V and A). This last has extensive jewellery
collections. The specimens on display in the Geology Museum have the
unforunate effect of making everything else seem a bit insignificant.
Don’t know about mineral shops in London. In Paris, a few years ago,
there were a few in the side streets in the area known as Isle de la
Cite, but they were selling at tourist type prices. Hav a good trip!
Kevin (NW England, UK)