Sealing rock?

[flitabout]

Ok so another post made me think of this. I am going to do a total break down and rescape. New plants, substrate, co2 system, and rocks. The thought just crossed my mind. I live in Pipestone and we have some of the most beautiful red stone I have ever seen, and I can go pick it up from almost any where around me. My son can't find his piece to test. It's just that at this time of year it's impossible to find the rough pieces and the only way to get it is to buy is and I am not buying a nice piece of pipestone for making pipes just to dump vinegar on it. So even if it tests bad for an aquarium, is there a way to seal it and use it anyway?
Also this is the stats on the rock I want to use.
Geologically, pipestone is metamorphic clay (silicate of alumina). The red color results from oxidation of trace amounts of iron. The formation of the soft red stone called pipestone or "catlinite" began about 1.2 billion years ago when oceans covered Minnesota.

 

[V227]

Unless your water is acidic, I wouldn't worry about any limestone content. I don't know much about pipestone rock or mudstone, other than its soft enought to carve. I'd.be worried that the rock might cloud up the tank. The traces of iron might not be good for the fish either. I've never sealed an object for aquarium use, but aquarium safe "poly" products are available.
My guess is the rock is probably okay, just research it further to be sure.