It's a 'handle with care' product. Quite mild, but don't eat it, breath in the dust, or rub it in your eyes. Like common salt, mostly harmless unless you are exposed to a lot of it. (If you think table salt is safe try rubbing the crystals in your eyes, eating a tablespoon a day for a month, or working unprotected in a salt processing plant for a few years.)
Metallic mercury is pretty benign too – unless you breath in the vapour. World of difference between playing with Mercury at room temperature for ten minutes and boiling the same quantity dry over a Bunsen, which is what unsupervised boys are likely to do!
Dave