A new grooming aid to me

I was watching Tipical MaryEllen on HGTV and she had a segment on dog grooming. Something I had never seen before looked like a cool idea.
The groomer used a lava rock to groom the short haired dog's dead hair out of its coat.
I went to the feedmill today and when I was there was looking around at the horse stuff. I don't have a horse, but was looking to see what sort of stuff they have that I could use for the other pets I have.
They had this square of lava rock stuff about the size and shape of a bar of soap. You use this to groom them, so I got it for the short haired dogs. It worked really well and got a lot of undercoat out of their hair.When I was finished their hair was all smooth and shiny. I used it on my Lab mix, beagle mix, and two other short haired dogs. It was so quick and I didn't get the static build up like I get with combs and brushes.
Has anyone else ever done thisn or heard of it before. The woman on TV said it can be used in place of a shedding blade. I think it works better.