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> > Now I have two new questions: What can people tell me about
> >Aragonite? I'm curious about its chemical composition, its buffering
> >capacity, and its possible use(s) and bendfits in a planted aquarium.
> >This is more intellectual curiousity than anything else, since I ass-
> >ume its possible benefits do not add up to its cost.
> Don't be fooled by the name. Aragonite is just calcium carbonate. It is
> the orthorhombic crystal form which forms at temps above 30 C. The other
> commercially important form is calcite. Calcite is hexagonal-rhombohedral
> and is formed at temps below 30 C. Aragonite has a lower melting point and
> is slightly more dense than calcite. However, chemically speaking, calcium
> carbonate is calcium carbonate.
That is all by the book, but a couple of relevant facts have yet to see
First, the dominant mechanism for the formation of aragonite on the
surface of the earth is biogenic calcification. Most of that is laid
down by corals, some by coralline algae, some by mulloscs.
Melting points and density of aragonite matter little, the fact that it
has a Ksp about a factor of two lower than calcite means that it
dissolves more readily in aquarium situations than calcite.
I'm at a loss to understand what the originator of this question meant by
cost of aragonite outweighing benefits. Last time I looked, it was
available for about 10^-1 dollar per pound at just about every pet store in
the US as "crushed coral" or "aragonite."
As far as using it in a planted tank... the main caveat is that it will
dissolve relatively slowly, and there is a ton of buffering capacity
there. If you put in too much, it will increase both the GH and KH of
the water (I've been reading this list too long.) How high might it
drive those values? Drop a pound or two into your tank, and move from
the freshwater planted world towards the rift lake world.