• Why is aragonite sand white, while coral rubble darkens?

  • Joseph8592

Why is aragonite sand white, while coral fragments darken? It seems like a simple question, but I can't find the answer yet. The bleached remains of coral are bright white, but after a couple of months, they turn dark, while the sand at the bottom of the aquarium is always white...

Jesse3979

The sand is constantly stirred and "licked" by bottom-dwelling inhabitants, such as polychaetes. Algae settle in the pores of the coral skeleton, which can only be removed with bleach.

Anthony

I agree with the highlighted point. The key word is in the pores. I believe that if you grind the white coral skeleton down to sand-sized particles, it will still darken due to its porous structure because algae settle in the pores of the coral skeleton. Based on this, I have a hypothesis that white sand is not made up of coral remains, but rather the skeletons of mollusks. The shells of snails are practically monolithic and have no pores. That's my assumption.

Denise

Not a fact. The shell of mollusks has a layered structure, and the pores are just fine.

Lauren

If you break a large shell of a mussel or oyster, you can see both the layering and porosity in the "cross-section."