How much dust is in Mars's atmosphere at ground level, and what's it made of?

I was thinking about the problems of fully automated robotic mining, and it occured to me that mining is a lot simpler if you don't have to move anywhere. For example, it's possible to mine the Martian atmsophere for carbon dioxide and water vapor just by pumping in the air and filtering out what you want.

Of course, there's the problem of dust, so you'll need to filter out the dust...

And that's when I had an "aha" moment. Why not mine the Martian atmosphere for dust? You could have a circular filter which constantly rotates past fixed "wiper blades". Accumulated dust falls from the wiper blades into a tube for processing.

Compared to a scooping robot, this mining robot doesn't need to move anywhere. It just sits and lets the dust come to it.

How much dust is available? Obviously, it will be different in a dust storm vs a calm day.

What is the dust made out of?

Thanks!