Why do some rocks absorb water and some do not?
The porosity is affected by the space between the particles which make up the rock, Loosely packed rocks such as sandstone will soak up water or allow it to pass through, while granite, because of its tightly intertwined mineral constituents, is non-permeable.
Dark rocks will absorb more radiant heat than light rocks, for the same reason that any dark object absorbs more heat than an equivalent light object. Light objects appear "light" to us because they reflect more light than objects which appear dark. Dark objects appear dark because they absorb more light and reflect less. However, dark objects will radiate more heat that light objects. Actually, dark rocks do NOT absorb more radiant heat than light…
I believe it is mean the activated charcoal or in common, activated carbon. Activated carbon (steamed charcoal under vacuum) had porous structure that can absorb many organic solvent, free chlorine in water and absorb smell. It was widely use in water treatment, some might leave activated carbon in fish tank to absorb organic waste and keep the water clean.