Sandstone I think?

I grabbed a really cool looking piece of sandstone from a buddy of mine. It would look great in my tank and provide two more caves for fish and such. I currently have it soaking in a tub of FW cause I wasnt sure if it would boost my PH or any other levels in my tank. My question is do I have to "cure" the sandstone like LR? It was in my buddy's FW tank years ago, but has been sitting outside for some time now, so I know its dirty. I know if I can put it in the tank eventually it turn into LR more or less, just wanting to know If it should be soaked for a good while, and if there are any dangers with sandstone in a SW tank. Thanks guys!

 

the only reason lr needs curing is because it will probably have die off from travelling...sponges etc. that piece of sand stone should be like base rock now. just add it... but maybe give it a good rinse

 

I was curious cause I did some research on the net, and seen yes and no as far as sandstone goes....Im gonna let that thing soak for a few days and go from there.