Definition of "powdery"

We were plowing through great deeps of powdery alkali dust that rose in thick clouds and floated across the plain like smoke from a burning house. We were coated with it like millers; so were the coach, the mules, the mail-bags, the driver—we and the sage-brush and the other scenery were all one monotonous color.

1870–1871 (date written), Mark Twain [pseudonym; Samuel Langhorne Clemens], chapter XXI, in Roughing It, Hartford, Conn.: American Publishing Company [et al.], published 1872