epsom salts baby yea!

Hi...

I'm wondering whether all Epsom Salts you buy are created equal. The reason being is the shopping center near my home sells Epsom Salts available in some conspicous aisle on the bottom row, sealed but dusty so it looks like its been around for some time and I'm the only guy to pick up a bottle in a long time. I bought it but have been pretty apprehnsive about using it b/c I figure that there might be a "better" brand out there whose bottle might have been less dusty? Are these fears unfounded and that all Epsom Salts are the same and there isnt much difference in quality vs. manufacturing time.