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Re: volcanic materials as substrate

Jos K. K. Liem wrote:
> I wonder If anybody have experience in using volcanic as a
> substrate.
> Amano uses for several tanks vulcanic sand.
> Volcanic soil is usually  very fertile.

For the most part volcanic stuff is just rocks.  Nothing special.  You 
probably want to avoid anything recently erupted, since it may be very 
unstable, acidic and contain sharp fragments.   With that said, now I'll 
blither on about the details...

There's really two common sorts of volcanic areas.  One would be like the
Columbia River Plateau in the US or the Deccan Plateau in India.  The
available material is mostly just dense black lava called basalt.  
Sand or gravel made from the basalt is pretty stable and probably safe 
for aquariums.

The other kind of volcanic area includes many island arcs like Japan and
New Zealand and also major mountain chains like the Cascade Mountains in
the US and parts of the Andes and central Mexico.  The rocks there are
much more diverse.  My area here in New Mexico (somewhat like east Africa)
has features of both. 

A fair part of the coarse sand, fine gravel and stones that I can collect 
out of the local river is of volcanic origin.  This stuff is not all 
created equally.

I'm fond of the rounded pebbles and stones of scoria and lava.  These are
either black or iron-red and full of bubbles, so they're fairly attractive
and much lighter than most stones.  Java fern anchors to it very easily.

Some volcanic material is mostly glass.  That includes obsidian (black and
glassy), pumice (solidified foam) and sometimes a kind of rock called
"tuff", which can look like anything from black glass to white chalk. 
Obsidian and pumice can be quite unique and attractive.  But natural
volcanic glass is impure and may not be as stable as man made glass. 
Using it in an aquarium - particularly something like a rift lake tank
with high pH - may give your water slightly elevated silica levels.  My
tap water is quite high in silica because of reactions between ground
water and volcanic material in the aquifer.  I'm not sure if there's a
problem with that (aside from having water deposits from hell). 

Sands and gravel composed of volcanic material might contain some of both
of those types.  Probably the largest component is just fine-grained,
somewhat weathered mixed bag of different kinds of tuffs and lavas. 
Smaller streams in volcanic areas will sometimes yield sand or gravel that
is all one color but larger streams will yield sand or gravel with a lot
of different colors and textures.  Very interesting to look at.  You might
want to pick out sharp pieces or the odd bits of obsidian (looks like
black glass) and pumice (floats when its dry), but otherwise it should
make fine substrate material. 

Soil derived from volcanic material is another thing entirely.  These 
can be anything from white clay to black sand, so its hard to generalize 
their quality as a soil.  Don't mistake recently erupted ash (like from 
Saint Helens) for soil.

Roger Miller

In Albuquerque, where all the volcanoes are now peacefully snow-capped.