The lighter areas of Rock 6 (A in the inset photo) are "fresh" surfaces, exposed when the rock was broken during collection. Surfaces exposed to the seawater for long periods of time (B) turn reddish brown due to iron-oxides that precipitate from the seawater and coat individual grains.

Collected on JSLII Dive 3464, Popenoe Coral Mounds, Blake Plateau (2567 ft).