Actually there are
two geological museums in Warsaw! I visited them both. Both have an overlapping collection and do not specialize to Poland only. Both have minerals, stones (petrology) and jurassic/dinasaur bone stuff. But only one of them has a nice collection of Amber, something that is intensively present in the stores in the rebuilt old town. Nice to visit, in Polish cafe's they have a lot of different Polish beer. Extremely tasty!!
The first one is the smallest, has two separate buildings and is called Muzeum Ziemi Pan,
Na Skarpie 20, www.mz-pan-pl(not the proper link, i will try to find it)
found it:
mz.pan.plThe second one is given below by Frank and lools like an university museum (what it is).
The overall quality is 'nice if you do not have something important to do' and there is limited English information. The entrence is (almost) nothing. The mineral collection is not so very special for a spoiled Strahler and most interesting are the Polish finds, since you are in Poland!