Hi Betsy,
does it have to be IN munich?
Do you know Bad Feilnbach?
Near to there is a lovely Dinosaur museum along with all things including rocks, stones, minerals ... etc
It is signposted from the nearest motorway junction (Salzburg Motorway) and is in a very small village called Kleinholzhausen, the museum is "Urweltmuseum"
Here is the link (if I'm allowed):
UrweltmuseumAdjoining the museum is a hotel / restaurant which serves wonderful "Hot Stone" cook 'em yourself at the table mixed grills and steaks!