Maintaining A Healthy Flock

Sevens Dust? I'm a new chicken owner (2 1/2 months now) and I was told by a friend that they dust their chickens with sevens dust to keep the mites off them. Is this ok to use on chickens? Our friend said he's been doing this for many years and it doesn't hurt them but I don't know. What's the opinion here?

Diatomaceous Earth, food grade. I use Pure Earth company on all my animals. If you use Sevens Dust use the 5% garden variety