would this make effect mgso4 to dry with

Not entirely sure, I know there are far simpler ways. I just microwave mine, it doesn't take long, much quicker than an oven, just nuke it until it's hard and chalky white. It should become fused together and hard, chalk- like.

brilliant orion!

ill keep this in mind, do you know if its as effective as breaking the chunks down to powder and baking further to ensure a flowing sand like quality? for some reason im always compelled to do so. but ill give this drying method a shot next time.

does it damage a microwave in anyway?

The microwave just heats the water, which then evaps from the heat.

Not enough heat to burn or damage the mgso

I would break it up into small chunks but not totally powder it, as you will block off most of it from the air, which may impair its ability to grab moisture from the air, but I can't back that up with data, just a hunch, I just smash it up a bit. Doesn't seem to damage the microwave none. One thing I'm wondering is if one could use this for the full process of drying mushrooms, simply adding fresh shrooms and the anhydrous epsom salt to an airproof container, dry them partially, re-nuke the epsom salts, and dry them further?