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The way to find out is to test it yourself. That's what I did.
The giveaway of its marine origin is the tiny shells found on the sieve. The Cretaceous Sea once connected the Arctic Ocean with the Gulf of Mexico, covering the great plains of North America. Sedimentation left this deposit of Diatomaceous earth in central Alberta, Canada. This sample contains enough clay that I was able to slurry it up, dewater it on a plaster bat and then prepare SHAB test bars to try it at five temperatures. At cone 10 (bottom right) the porosity is 62%! And the LOI is 32% (others can go as high at 50%). Why? Raw diatomaceous earth contains physically bound interlayer water, it leaves by ~100–300 °C. It also contains structural hydroxyl water (in clay minerals or hydrated silica phases). This “chemical water” burns off between ~400–700 °C. And, organic matter from ancient organic material from algae, plants, or soil contamination also burns out between ~300–800 °C (as CO₂ and other gases). Finally, the carbonates (e.g. shells shown here) decompose around 700–900 °C, releasing CO₂. That alone can cause a big weight loss.
Note the test bars under it. Where this bar was sitting there is glassy deposit. What is that? Diatomaceous earth is mostly amorphous silica, but it almost always contains alkali and alkaline-earth impurities and sometimes boron. The latter can literally drain out, as a liquid. However here, the alkalis have volatilized (vaporized) or form alkali-rich fumes. These landed on nearby surfaces to react with the other test bars to form a thin alkali-silicate glass layer (similar to what happens in soda firing).
| Materials |
Diatomaceous Earth
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