Geoscience Reference
In-Depth Information
Additional health-related roles of gastroliths include their possible use as min-
eral supplements, especially if these are calcium-rich rocks, like limestone. Read
the label on the bottle of nearly all over-the-counter antacids, and under “Active In-
gredients” you will see calcium carbonate listed. This means the antacids are made
of either calcite or aragonite, which also happen to be the primary minerals in most
limestones. These minerals, once they encounter and react with low-pH acids in
your stomach, increase the pH, making it less acidic and more basic. In this reac-
tion,thecalciumcarbonatedissolves,liberatingcalciumfromitsbondswithcarbon
dioxide, which is released as a gas. (This is where former geology students fondly
remember identifying limestone in lab exercises, in which they repeatedly dropped
diluted acid on these rocks and satisfyingly watched them fizz.) How would we
knowthatabirdorotheranimalatelimestone?Wewouldnot,unlesswecaughtitin
the act. The limestone, once inside an animal's stomach, would quickly disappear,
leaving no sign it was ever there, except for maybe sudden releases of gas.
No firm evidence supports the notions that gastroliths are used for other self-
medication,suchasforre-introducinggutbacteria,ordestroyingparasites—thelat-
ter the internal equivalent of crushing a tapeworm between two rocks. There is also
noreasontosupposethatstonesareusedtoeitheralleviateorincreaseappetite,thus
fulfilling a recipe for “stone soup.”
Nonetheless, a few birds, mammals, and even humans sometimes ingest clay
or soil as a digestive aid, a practice called geophagy. This is not such a crazy prac-
tice, as some clay minerals have adsorptive properties, in which toxins latch on to
the minerals and are later passed out of the body. For example, kaolinite—a white
claycommoninEoceneandCretaceoussedimentarydepositsofGeorgia—hasbeen
longusedformedicinalpurposes,datingbackfromitstraditionaluseinWestAfric-
an societies, and then continued in slave communities in North America. This rem-
edywasusedmorebroadlyinKaopectate™,acommercialliquidusedtotreatstom-
ach ailments, in which kaolinite was an active ingredient. However, ornithologists
who have studied geophagy in South American birds—such as macaws and par-
