Chalk for weathering?

Plain chalks are kind of hard to use, they tend to blow away easy. However, I use earth tones (browns, tans, reddish browns), plus white, gray & black.

Weathering powders are much easier to use. The powder sticks better.
 
I use artist pastels. I find them to be far cheaper than model railroad weathering powder sticks...but just as effective. Just don't forget to dullcoat it when you're down...to avoid it falling off.