the intrinsic nature of the blue-white and other light-colored materials in the scene?

Maybe I haven't followed along closely enough, but there doesn't seem to be any question that the white and light-colored material is "natural" and not a curious byproduct of grinding and crushing.

I note there are several rocks in the scene with little globes on stalks. I don't know what was crushed on the right side of the scene to produce the blue-white material, but it may have been one of these exhuberant and festive formations that may only appear ruddy brown when coated with the omnipresent dust. Something was crushed, however, and to me the result looks like salt.

The large rock may have been "bleached" over time. It seems that some surface materials have either a very thin light-colored coating or they somehow "bleach" in the sun; the material just below the surface can be quite dark. Whether that's the case here, I don't know.

Cheers, BRFelix