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Re: rocks in the aquarium

Rober H wrote:

> The rockery that I
> purchase from actually packages the rocks specifically for aquarium use. The
> types include many forms of quartz, (which I already mentioned) and others
> identified as Rainbow, Z-Lite, Lava rock, (we all know what that is), Tufa,
> Picture stone, Onyx, Obsidian, Pagoda stone, Travertine, Mariposa, Sodalite,
> petrified wood, slate, sandstone and Geodes. Do any of these send up any red
> flags?

Rainbow       -- trade name, I don't know what it is
Z-lite        -- ditto.  Something to do with zeolite?
Lava rock     -- might be awfully jagged but otherwise it should be fine
                 unless it has a whitish calcite coating on it.  Here I 
                 like the cobbles and pebbles that have rolled down the
river;                  they come in black and red.
Tufa          -- a low-density, usually calcareous spring deposit. 
Mostly                      calcite and will raise alkalinity and GH. 
Can also be 
                 called sinter, though I usually reserve that term for a
                 spring deposit that is mostly silica.  See travertine.
Picture stone -- trade name.  I've seen this, but I didn't look closely
                 enough to figure out what it was.  I think I read some-
                 where that it is from a weathered volcanic ash deposit.
                 If so, then it should be safe.
Onyx          -- True onyx should be safe, but see under travertine.
Obsidian      -- black volcanic glass.  If it isn't too sharp then it
                 be safe.  As "apache tears" it makes an interesting 
                 substrate addition.
Pagoda stone  -- trade name.  I have no idea.
Travertine    -- a relatively high-density spring or cave deposit.  
                 Mostly calcite, so it will raise alkalinity and KH.
                 "Mexican" onyx or onyx marble is a kind of travertine, 
                 often dyed and/or coated with something.  It can
be                            distinguished from true onyx because it is
soft enough to                      scratch with a knife and true onyx
isn't.  Mexican onyx 
                 also fizzes when you put a drop of strong acid on an 
                 uncoated surface, and true onyx does not.
Mariposa      -- trade name.  I don't know what it is, but I think the
name                     means "butterfly".  I don't suppose that's very
Sodalite      -- A typically blue or gray silicate.  An unusualy
                 but if it's pure it should be fine.
Petrified wood-- almost always safe.  There is some bizzare petrified
                 out there that you probably won't see that's
                 with things like chalcocite (metallic grey copper ore)
                 carnotite (bright yellow uranium ore).
Slate         -- should be safe.  Some varieties contain calcite, others
                 may contain pyrite.
Sandstone     -- usually safe, but test with acid to see if it is
                 with calcite.  If so then it can raise KH and GH.
Geodes        -- Usually fine if lined with quart crystals.  Some
                 calcite and these may tend to raise alkalinity and GH.
                 I've even seen some lined with pyrite.  They're neat
                 the mantle but they probably shouldn't be in the

So tufa and travertine raise the flag, and a few others need cautions. 
Tufa and travertine would probably be fine in a marine aquarium or rift
lake tank, but people probably don't want them in with their apistos.

Roger Miller