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Rocks and Decorations


  1. FAQ on Rocks/Stones
    by (patrick timlin) (17 Aug 1995)
  2. FAQ on Rocks/Stones
    by (18 Aug 1995)
  3. decorating a tank..pointers?
    by Shawn Young <srly.dont_want_no_spam/> (Sat, 24 Jan 1998)
  4. Aquatic Plants Digest V3 #76
    by "Dennis J. Harney" <harneyd1/> (Tue, 9 Feb 1993)
  5. Petrified Wood - Inert Rock
    by "Roger S. Miller" <rgrmill/> (Tue, 12 Jan 1999)
  6. RE: Home Depot
    by "James Purchase" <jpurch/> (Wed, 21 Apr 1999)
  7. Lead weights
    by "Jeff Taylor" <taylorj/> (Sun, 2 Apr 2000)
  8. Rocks for the aquarium
    by "Robert H" <robertpaulh/> (Sun, 15 Jul 2001)
  9. rocks for the aquarium
    by "Roger S. Miller" <rgrmill/> (Mon, 16 Jul 2001)
  10. rocks for the aquarium
    by "Vincent Chan" <vchan/> (Tue, 17 Jul 2001)

FAQ on Rocks/Stones

by (patrick timlin)
Date: 17 Aug 1995
Newsgroup: rec.aquaria

Tuomo ( wrote:

: I've been looking through the FAQs , books , etc. on types
: of rocks that are definitely safe for freshwater aquariums and

: What I want to do is build a 65G tank with a lot of rock formations using 
: different types of rocks ( slate, marble, etc.dark stones  ) but don't
: want to deal with excessive water hardness from maybe an unsuitable type
: of stone....

Slate is fine but marble is not.  MArble is too soft and will leach into
your water.  Granite is also good.  One trick to test rocks is to put a
few drops of vineger (sp?) on it.  If after a few minutes it starts to
foam, then don't use it in the tank as this is an indication that the
rock will slowly dissolve in your tank.  Also avoid any rocks that
appear to have any veins of metal running through them.

Patrick Timlin

From rec.aquaria Thu Aug 17 23:46:22 1995

FAQ on Rocks/Stones

Date: 18 Aug 1995
Newsgroup: rec.aquaria

The safest rocks for a freshwater tank are lava rock, slate, quartz, onyx, and
pertrified wood.  Do not trust a rock not to leach or dissolve simply because
the petstore told you it was safe.  I was sold a rock once that I was told was
"aquarium safe" that ending up dissolving in the tank and playing havok on the
hardness of the water.  If you doubt the safety of the rock do not use it.  Try
to stick to the above listed rocks and to rocks that are listed in a good book
on fish.  Good luck with the tank.
* Melissa Danforth * S. Amer. cichlidiot and *
*  "And as imagination bodies forth              * general fish enthusiast *
*   The forms of things unknown, the poet's pen  *    "Four legs good,     *
*   Turns them to shapes . . ."                  *       Two legs baaad."  *
*     A Midsummer Night's Dream  V.i.14-16       *  The sheep Animal Farm  *

decorating a tank..pointers?

by Shawn Young <srly.dont_want_no_spam/>
Date: Sat, 24 Jan 1998
Newsgroup: rec.aquaria.freshwater.plants

I'd just get lots of slate (maybe roots, coconuts, some 
appropriate river rocks), and start building. You might want
to dig up some of the plants so you can put a largish piece
down to act as a base and distribute the weight wherever you
decide to build. Probably not an issue (I do or I don't, as
the mood and materials and the picture I have in my mind dictate).

Making things stable... Use angles and basic physics of lever
arms, etc. I'm not suggesting you learn a bunch of physics, but
most people know that if you have a small amount (less than half)
of an object's weight resting on a surface, and the remainder of 
the weight hanging in space (or water in this case), the object 
will tip over or at least be very unstable. Use long, narrow,
thick pieces of slate or root to create a ledge upon which the
first cave or ledge will rest. Set them out from wherever the
base of the ledge piece will sit, so that about 1/3 of the
ledge pice will overhang. Dig these in so they are solid in the
gravel, preferably retsing on the bottom of the tank of the
base piece of slate you have buried. Then dig the back end of
your ledge into the gravel behind this structure, resting it
on top. There's your first cave. 

Start wide at the bottom and get narrower/shallower to the extent 
that makes sense and stays stable as you build up; if any building 
up is required. A single very large cave I put in a friend's tank 
is home to his largish leopard pleco, and has a few very small 
terraces above. It's hard to clean, but the plec loves it and 
nobody else is allowed to visit. Small thin pieces of slate
placed on an angle strategically in a gravel bed can be used
to shore up "hills", etc.

As you build up, fill and form layers with gravel around the
edges to suit your taste and establish stability. Use roots to
give the appearance of a tree growing down through the rocky
structures below, coconut shell halves with holes or grooves
cut in them (so that fish can use them as caves for breeding
or whatever) to prop up ledges and give the appearance of a
collapsing stream bank propped up by debris from nearby
trees, etc., etc. Build in "pools" of gravel to plant up,
if that makes sense.

Most importantly, have fun. Practice makes perfect.

I have never seen the need for silicon in any of these structures
if common sense prevails, and time and care are taken. Building
them this way makes it very easy to rearrange here and there 
until it perfectly suits your taste. I'd suggest doing all that
rearranging _before_ your fish take up residence on that massive
root structure in the middle of the tank, or the little cave at
the top of a gradual terraced incline.



Aquatic Plants Digest V3 #76

by "Dennis J. Harney" <harneyd1/>
Date: Tue, 9 Feb 1993

For any grad students out autoclave works wonders on drift
wood.  Pop it in on wet cycle for 10 or 15 minutes and do not let it go into
a dry cycle.  The high pressure steam penetrates every bit of the wood.  It
comes out soaked and very hot.  I pop it right into a bucket of water and
change the water 2 or 3 times over a day or so.  This is faster than the
normal week it takes for it to absorb enough water to sink.  Fast, clean,

Dennis J. Harney
Miami University Botany Dept.
from Oxford, OH, home of the municipal chlorine spike.

Petrified Wood - Inert Rock

by "Roger S. Miller" <rgrmill/>
Date: Tue, 12 Jan 1999

On Tue, 12 Jan 1999, Tom Wood wrote:


> But I was most surprised at his recommendation to use petrified wood in
> a planted tank.  Is petrified wood always non-calcerous?  Is it always
> inert?  What other rocks are tank safe?

Petrified wood is almost always made up of microcrystalline quartz.  It's
very inert and safe to use in an aquarium.  That said, let me point out
some exceptions.  Calcite (calcium carbonate) is almost ubiquitous so
there's always a likelihood that a bit of petrified wood that you pick up
(or buy) somewhere is going to have some calcite in it or on it - the
calcite is not usually a large part of the petrified wood and usually just
washing the thing off will get rid of most of it.  On rare occasions there
are examples of petrified wood that's been petrified with something other
than quartz - I've seen or heard of wood petrified with carnotite (a
bright yellow uranium mineral), chalcopyrite (usually a metallic-looking
copper ore) and a few other things.  Those examples are real geologic
oddities and you'd probably have to go *way* out of your way to find them.

It's fairly difficult to generalize about what rocks are safe in an
aquarium.  Petrified wood is probably safest of all; all forms of quartz
are safe.  "Granite" will usually be safe, as well.  As generalizations
go, it's probably fairly safe to say that a stone (pebble, cobble,
whatever) that's been rounded and polished in a stream or on a beach is
probably going to be safe to use.

Just about any time you use a mined or quarried stone you are taking some
risk that it will contain chemically unstable minerals that will do
something unpleasant in your tank.

Some specifics you should avoid:

	marble, limestone, dolomite, shells, coral skeletons or anything
similar (the preceding all contain calcium and/or magnesium carbonates and
fiz in acid - the dolomite you might have to scratch before it fizzes

	sandstones (rocks that look like cemented or compacted sand - they
often are cemented with calcite and will fizz in acid),

	anything with a shining metallic luster like "fools gold"  (these
are usually sulfides that can go through acid-producing reactions and/or
release metals into solution),

	coal (pretty under water, but it's often treated with oil to
suppress dust and it often carries a high level of sulfur and metals that
can be a problem if released into the water).

I'm sure there's lots of others.

You can find a lot of beautiful stones at rock and mineral shops, and some
of those can be great aquarium decorations, but personally I prefer
petrified wood and the look of stream-rolled stones.  But some
probably safe examples that you might find at a rock shop are:

	Varieties of microcrystalline quartz (for example jasper,
chalcedony, agate, sard, carnelian),

	jade (attractive and inert but IMHO the green color of jade
clashes with the greens in plants),

	all forms of crystalline quartz (e.g. rock crystal, amethyst,
citrine, rose quartz, smokey quartz).

Fossils look very cool, but many contain calcite or pyrite and
shouldn't be used and some are varnished for preservation and shouldn't
be submersed.

Rock shop owners and/or sales people might be knowledgable enough
to help you figure out what will be safe in an aquarium.  Ask them.

Roger Miller

RE: Home Depot

by "James Purchase" <jpurch/>
Date: Wed, 21 Apr 1999

>I was reading on the tropica site ( about how they
>attach java ferns and other plants to
>lava rocks and thus have "portable plants". I was at
>home depot yesterday in their gas grill section and noticed they sell a
>bag of lava rocks for $4. Since
>these are just dumped into a grill, I can't imagine them being anything
>other than plain rocks. I would guess they'd be safe for a fish tank.

They are just "plain rocks" and they make excellent holdfasts for Java
Ferns. I've used them for years with absolutely no problems.

James Purchase

Lead weights

by "Jeff Taylor" <taylorj/>
Date: Sun, 2 Apr 2000

Mark said:

> Instead of lead weights I have found common rock to be very effective.
> This method involved some work, but it remains very effective.
> First, locate some flat rocks about 1/2" to 1' thick.  Using a drill
> press and a 3/16ths concrete drill bit, drill a hole in the rock.  Keep
> the tip wet and slower rotation speeds are more effective than faster
> ones. Plan ahead to be sure that the rock will not interfere with other
> plantings in the aquarium.

If you want to find a great supply for these rocks in attractive 
styles, see if you have a local Pier One Imports and ask for 
Chinese Lucky Stones.  These are 1 kilo (2.2 pounds) of polished 
river stones in a little mesh bag.  Cleaned, polished and attractive 
for about $3 a bag.  The stone range in the 1/2" to 3/4" thick range 
and Mark is right...they are perfect for drilling and attaching plants 

Jeff Taylor --- Paying good money for rocks in Louisiana

Rocks for the aquarium

by "Robert H" <robertpaulh/>
Date: Sun, 15 Jul 2001

Rocks in the aquarium

I have been getting a number of questions about what type of rocks are best
for use in the aquarium, and I thought I would share this information with
the group, as I am also working on a more detailed article of this subject.

Quartz is an interesting mineral because it comes in many variations.
Literally hundreds. Its principal componant is Silicon dioxide. This is
where your computer chips come from.

These are the main varieties:

 A) Chalcedony- Microcrystalline variety
Scientifically, the term "Chalcedony" refers to any type of microcrystalline
Quartz.  These types include:
Agate - Banded variety
Carnelian - Reddish, transparent to translucent variety
Onyx - Banded variety in which the banding lines are straight and parallel,
and consistent in band size.
Jasper - Opaque variety of Chalcedony that occurs in all colors.
Tiger's Eye - Pseudomorph of Quartz after fibrous Crocidolite.
Chrysoprase - Apple-green variety
Bloodstone (or Heliotrope) - Dark green to greenish blue variety dotted with
small, red, bloodlike spots.
Sard - Brownish to brownish-red, transparent to translucent variety
Sardonyx - Banded variety with straight parallel bands of brownish to red
alternating with white or black bands.
Flint - Massive, uniformly colored variety that is somewhat impure.

B) Amethyst - Purple variety
C) Citrine - Yellow to yellow-brown variety
D) Rose Quartz - Pink variety
E)Rock Crystal - Colorless, transparent variety
F)Smoky Quartz - Brownish-black, "smoky" variety
G)Milky Quartz - White, translucent to opaque variety
H)Rutilated Quartz - Quartz with golden-yellow, needlelike Rutile inclusions
I)Aventurine - Opaque, massive Quartz containing small mica, Hematite, or
Goethite scales which cause a glistening effect.

Again, despite its color or form, (crystal, microcrystalline,
massive,nodular ) its still primarily silica. This will not alter the water
chemistry of your aquarium. Quartz can appear in rocks or Geodes where other
minerals such as Calcite are present, which will alter the pH in water.
Calcite consists of Calcium carbonate, commonly with some impurities of
either iron, magnesium, manganese, and occasionally with zinc and cobalt.
Calicte reacts to acid, so to test for it, simply apply drops of muratic
acid on it and if the rock fizzes, then Calcite is present. Rocks sold as
quartz or black onyx, or crystals  ordinarily are pure quartz mineral, not

I particularly like Onyx and Rose quartz. "Zebra rock", a quartz agate, is
also interesting and commonly sold for aquarium use.

Black Onyx is jet black, shiny and has bands of white. It may have some
spots of dull gray. What I really like about this rock is algae tends not to
grow on black objects! Put a very light colored plant in front of it, such
as E tenellus, and you have quite a sharp contrast

Rose quartz is light pink in color. Deeply colored, massive Rose Quartz is
found in numerous localities in Minas Gerais, Brazil, and the best American
material of this sort is from the Black Hills of South Dakota (near Custer,
Custer Co.).

(Massive - Term used to describe a rock or mineral that has no particular
shape, either because it is non-crystalline
it is composed of tiny, unorganized crystals it is a shapeless fragment of a

Quartz is not particularly heavy. I like to work safely with rocks that can
fit in the palm of my hand. This size generally works well in any size
aquarium for accent solitary aquascaping or for stacking or creating walls.

OK, onto things other than quartz:

Petrified wood:
Petrified Wood is wood chemically replaced by a mineral substance. The
replacement is usually Chalcedony ("silica"), but Opal and other minerals
are also known to replace the wood. When the wood becomes petrified, its
original mold remains intact, but an entire new substance takes the place of
what was once wood. In the Petrified Forest National Monument in Arizona, an
entire forest was transformed into petrified wood. Remains of this ancient
forest can be seen in the huge silicafied logs that are found in the area.

Shale, Slate
Slates are formed from clays, shales, volcanic ash, and other fine-grained
rocks. Minerals present are quartz, sericite, chlorite, some graphite,
titanium oxide, and iron oxides.

Sandstone is a sedimentary rock made of sand-sized grains of minerals,
mostly quartz and feldspar, or older rocks held together by one of several
types of cement or  a fine, muddy matrix. Sandstones vary greatly in color,
composition, texture of grains, degree of cementation and layering. Common
colors include grey, tan and red.

These are just a few examples of the many rocks and minerals that can be
used for decorative purposes in an aquarium. "Pagoda" rock is another,
commonly found in some aquarium stores, but I have not been able to find any
information of its make up. It is quite heavy and has a layered look to it.
I havnt yet done an acid test on it. If anyone has any information on this
type of "rock", please forward it to me.

I hope this information is helpfull. Rocks and shells that definetly will
affect water parameters are limestone and those containing seashell or

Best regards

Robert Paul H
 Quality plants, rocks and wood, and PLEASANT conversation! Now with a live
help line.

rocks for the aquarium

by "Roger S. Miller" <rgrmill/>
Date: Mon, 16 Jul 2001

Daphne Freeman wrote:

> I found Robert's info on rocks very interesting but have a question.  I have
> been considering adding some slate to my tank.  I haven't already since you
> couldn't see it though the green water!!  Anyway, it is black slate with
> deposits of rust-red in places. You can rub it off with your finger.  The
> "deposits"  grow in the aquarium and easily crumble into a mess if you rub
> across them in the water.

It's a somewhat-educated guess, but probably your slate contains a
little pyrite in microscopic grains.  Under water the pyrite oxidizes
and produces brownish iron oxide stain.  Small amounts of pyrite in a
rock aren't much of a problem but large amounts of pyrite can be a
problem, especially in poorly buffered water, as the oxidation process
liberates a lot of acid (as in acid mine drainage).

I have a couple other things to add to Roberts' descriptions.

Classically, onyx is a form of silica, and would be safe for an
aquarium.  Most of the onyx I see for sale is actually "Mexican onyx",
which is actually a sort of travertine and composed mostly of calcite. 
It isn't any better for an aquarium than is a chunk of limestone.

Sandstone is made of sand grains cemented together and it's mostly safe
stuff. The cementing material in some sandstone is calcite, which again
isn't particularly good for an aquarium unless you actually want your
hardness and alkalinity drifting upwards.  You might want to give it the
acid test; a sandstone cemented with calcite will fizz under a drop of
strong acid.

Metallic-looking minerals like pyrite (fool's gold) or galena need to be
avoided.  Metallic-looking minerals are usually sulfides, but can also
be arsenides, selenides or antimonides.  They can oxidize under water,
releasing  acids, potentially toxic metals and other solutes.

In fact, mined rocks in general may cause problems because they can
contain small amounts of soluble or reactive minerals that are removed
from rocks -- like stream-rolled stones -- that have been exposed at the

Being a geologist I have a long-standing interest in rocks and I've
often kept exotic-looking rocks in my tanks.  Some are aesthetic
disasters.  Of course, aesthetics is a rather personal matter, so there
are few rules.  There are some pretty simple things to keep in mind,
though.  Mostly, remember that not all colors go with green.

I used to keep a large chunk of jade in one of my tanks.  It never
looked right and after a while it dawned on me that the bluish-green
color of the jade clashed with the chlorophyll green of the plants.  I
also have a tank with a pile of slabs and chunks of bright red jasper. 
Same thing.  It clashes.  But it's also home for an old red-finned
botia, so I leave it there.
Petrified wood is great, and it's generally a safe and interesting
rock.  Incidentally, I think that collecting any petrified wood from
Federal land is illegal and collecting it from the Petrified Forest can
cost you a lot of money.  Some petrified wood is brightly colored, and
some of those shades don't work well with green plants.  I still have
some petrified wood (from Texas) in one of my tanks that is shades of
yellow and orange.  It stands out. The more plentiful petrified wood
from Arizona and New Mexico comes in a fairly wide range of colors, but
many are similarly bright and clashing colors.  If you want to use
petrified wood then it's probably better to use stones with more neutral

I think Amano pointed out in his first book that jagged rocks looked
unnatural in an aquarium, and that rounded river stones produce a more
harmonious effect.  I agree completely with that idea.  River stones
also have the advantage that they usually have fairly smooth surfaces;
there are few crevices and pits for algae to get a hold in where your
algae-cleaning crew can't get them out.  As a result, smooth stones stay
looking better under water then do rough or jagged stones.

There are a few rocks that I've seen for sale in the aquarium trade that
have no business in an aquarium.  Gypsum stands out as a great example. 
It comes in many forms, and at least three forms can be quite beautiful;
these are alabaster, satin spar and selenite.  Alabaster is fine-grained
and usually white or pink. Satin spar is shimmering white or pink
parallel fibers, usually filling a vein in other rocks.  Selenite is a
clear crystal and can be very large.  All of these forms are just gypsum
(calcium sulfate dihydrate), which is quite soluble.  It will gradually
disappear in your tank, and send the hardness sky-high.  It's also very
soft, so all of these forms can be detected because you can scratch them
with your thumb nail.

Rocks.  There's always more to be said about rocks.

Roger Miller

rocks for the aquarium

by "Vincent Chan" <vchan/>
Date: Tue, 17 Jul 2001

Another angle to look at rocks for aquarium may be from the point of overall
position and color/texture. Certain types of rocks works better in certain
settings. An example is sharper-edge, complex grain texture rock works may
well with brightly colored stem plants. Smoother, darker rock may work well
with ferns and crypts. The color of the substrate may also influent the
color choice of the rock. And of course we all have seen beautiful tanks
using nothing but rock formation as focus element, so in that case, the
shape and placement of the rocks will also be important.

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