Rock collector shops in Houston?

I'm a rock and mineral collector and looking for good sources to add to my collection. Yes, I know how to search Google, but my experience is that the best shops are sometimes hard to find and unlisted. There's probably a couple tucked away in the Harwin Drive import district that I don't know about. Places like The Museum of Natural Science have some, but they are overpriced with a poor selection. The spiritual crystal and jewelry/gem shops are not the places to find these.

If you know of any good shops for rock collectors in the Houston area please share.