From Dr. Ron Shimek's website
"The organisms do not care about the sediment mineral composition, only the particle sizes and shapes. Most aquarists use the commonly available aragonitic sands to "provide a calcium reservoir." Additionally their bright white color is often aesthetically pleasing. However, if the system's pH and calcium concentrations get low enough to dissolve significant amounts of the sediment there are some very severe problems and all the sand in the world won't help. Very successful tanks may be set up utilizing black lava sand, or fine siliceous sand, as long as the grains are of the appropriate size. There is some concern that siliceous sand will fuel diatom blooms, but such blooms may be controlled by the appropriate grazers."