black sand

[GaryP]

Steve,

I would think the sand would have small holes in it from volcanic gases. These holes may be microscopic but could be large enough for bacterial colonization in a DSB. I don't know that the resulting surface area would necessarily be larger than that produced by the pores in aragonite. In general, the more surface area you have, the more bacteria you will have. That's how bio balls work. Their shape is designed to maximize surface area for basterial colonization. This is pretty much all theoretical I would guess. You wouldn't have any way to measure bacterial colonization on a hobbyist level.

I have read that volcanic rock is not recommended for aquarium use because of toxic, heavy metals present in the rock. However, I would think a few thousand years of surf beating on the sand would leach out any water soluble metals present in the sand. Most of the volcanic rock you see in LFS is man made "pumice" and not of volcanic origin.

Gary

[Nano_Steve]

very interesting. i did not know that about pumice, i thought for sure that even pumice stones like those used for bathing were from volcanic activity of some sort.

on second thought, pumice is a ton heavier than volcanic rock, i remember going to the black miles in new mexico where its just a long stretch of volcanic rivers that have since cooled and the stones were deceivingly light. i picked up a rock that was about the size of my torso! :O

-steve

again i really appreciate this discussion, some great info and lots to think about. though i have to admit i am leaning towards having this black sand in my tank mainly for looks. :?

[GaryP]

Steve,

The density of volcanic rock can vary considerably. Some "pumice" can actually float because of the air spaces trapped inside. Other types are completely solid. It just depends on how much gas the volcano produces during the eruption. No two volcanos are alike. Black sand is the result of degradation of this volcanic rock. OK, enough geology for today.

Gary