All being well, my sister is now the proud owner of a lump of rock. I'm not exactly sure what sort of rock it is, and probably wouldn't spell it correctly if I did, but it's a really nice and interesting green colour.
It's also an odd shape, which made the request I built a stand for it to sit on a bit of a challenge. A bit of web surfing provided some ideas, but most of them didn't seem quite big enough, or I had to buy the things in bulk. I reckoned that I could make one myself however.
The wooden base came from eBay, a nice piece of oak for a few pounds. The 4.5mm diameter brass rod is from Eileen's Emporium. This cuts well with a tube cutting tool, you even get a nice chamfered end that only takes a tiny amount of cleaning up with a file.
The rear support was bent in a vice, not as neatly as I'd have liked (it looks worse in the photo) but as this is hidden by the rock, I could live with it. Holes needed to be vertical so I dug out the pillar drill. No glue required, just firmly pressing the rods home with a vice or long clamp.
Finishing touches involved Brasso and some metal lacquer to save future polishing.