Origin:  Vermiculite comes from mines all over the world.  The closest mines are Virginia and South Carolina.  Vermiculite processors take the vermiculite ore (hydrated mica) and heat it very hot.  The water (the hydrated part) expands and makes the vermiculite expand.  It expands 2000% to 3000%.

Name:  When the ore expands it “exfoliates” (separates into many, many layers, or pages) and grows long and worm-like.  Thus the name vermiculite.  As in vermiculture -- the growing of worms.  Or vermicelli – pasta shaped like worms.

Holds Water:  The uncounted layers of vermiculite enable it to hold lots and lots of water – 200% to over 300% of its own volume.  The water adsorbs (not absorbs) onto the many surfaces and becomes available to terrestrial plant roots as needed. 

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Damp vermiculite -- preferred by tarantulas world-wide.

Tarantula Substrate:  Vermiculite’s high water holding capacity makes it ideal for tarantulas.  It provides the humidity they prefer.  It’s light and easy for the burrowers to dig into.  It’s sterile and very inexpensive, which makes vermiculite economically easier to replace when it gets dirty.

Lizard Substrate:  Many small lizards (and some snakes) like to burrow or dig into their substrate.  Give them a tray or box of damp vermiculite -- way better than peat moss.  The humidity it provides encourages a better shed in tarantulas and reptiles.

Terrarium Substrate:  Vermiculite mixed with gravel makes an excellent substrate in which to grow bog plants.

Disadvantages:  The brown to dark brown color of vermiculite is not exactly eye catching.  It also enables many critters to disappear into the woodwork – great for the critter, not so hot for the keeper/observer.

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Vermiculite -- aquatic plant roots like it, too.

Aquatic Plant Substrate:  The multi-layered structure of vermiculite gives it a high cation exchange capacity.  This means it frees up and makes available the trace elements many plants need to grow abundantly.  Some lazy stingy time-saving aquatic gardeners add vermiculite to their substrate and totally eliminate the use of fertilizers and/or carbon dioxide injections.

Disadvantages:  When you use vermiculite in your aquarium, you need to waterlog it or it floats like a cork.  So you need to plan ahead.  You need to soak it at least three days.  A week works better.  Still, some of it will take even longer to sink.  Store this obstinate lot in a plastic bag and use it later.  It’s sterile and inorganic so it will not spoil.  Historical Note:  Old-timers used peat moss the same way.  Peat moss takes even longer to waterlog AND it turns your water brown -- sometimes dark brown.  The fish love it.  Fish observers hate it.

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If you vacuum your gravel, your "layers: get totally mixed.

Layer Your Vermiculite:  You gotta sink your vermiculite and keep it sunk.  You want your vermiculite on the bottom where the roots are.  You need to hold it down with a layer of fine gravel atop it (about an inch).  If you don’t cover it, your fish will constantly send it flying throughout your aquarium every time they make a mad dash for whatever piscatorial purpose trips their trigger.

Hard to Clean:  Anytime you start using your gravel vacuum cleaner, your vermiculite starts migrating along with any detritus you actually want to remove.

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Plant roots cling to the gravel and vermiculite they encounter.

Another Advantage:  In addition to the automatic fertilization mentioned earlier, vermiculite makes your substrate “fluffier” and more root-friendly.  When used with B-B sized gravel, vermiculite encourages root growth.  Good roots mean better leaves, faster growth, and better looking plants.

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Any loose vermiculite settles all over everything.

Other Caveats:  Avoid using vermiculite with cichlids (which dig or knock your substrate around).  Ditto with plecos and digging catfishes. 

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Java lance fern grown on pure vermiculite.

Last Word:  Want to avoid all the fiddling around with vermiculite in your aquarium?  Experiment.  Put some vermiculite in a nylon bag and drop it into your outside filter box.  You can get some of the fertilizing advantages of this versatile substance just by having it in your water.  LA

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