Diatomaceous Earth
Hydrated amorphous silica (SiO2·nH2O, diatom frustules)
Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.
- Mohs hardness
- 1-1.5
- Color
- White, cream, to pale grey
- Type
- sedimentary
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Overview
Diatomaceous earth (DE), also called diatomite or kieselguhr, is a soft, lightweight, porous sedimentary rock composed almost entirely of the fossilized silica shells (frustules) of diatoms, microscopic single-celled algae. The countless tiny, intricately structured shells make it extremely porous and chemically inert.
When crushed it forms a fine, chalky white to cream powder. Its remarkable absorbency, abrasiveness, and filtering ability give it a huge range of industrial and household uses. Major deposits occur in the United States (notably California and Nevada), as well as in many lacustrine and marine basins worldwide.
Formation & geology
Diatomaceous earth forms from the accumulation of diatom shells on the floors of lakes, seas, and other water bodies. Diatoms build their cell walls from silica extracted from the water; when they die, their durable shells sink and pile up over thousands of years.
Where conditions favor abundant diatom growth, such as nutrient-rich lakes and upwelling marine zones, and where dilution by other sediment is minimal, thick beds of nearly pure silica shells accumulate. Burial and gentle compaction turn these deposits into soft, friable diatomite. Both freshwater (lacustrine) and marine deposits exist.
How to identify it
Diatomaceous earth is recognized by being extremely lightweight, soft, and chalky, usually white to cream. It is very soft (hardness about 1-1.5) and crumbles easily into a fine powder that feels gritty yet light, and it can absorb large amounts of liquid.
Despite being made of silica, the bulk rock is soft because it is a loose mass of tiny porous shells. Under a microscope, the diatom frustules show beautiful geometric patterns. It does not fizz in acid.
Look-alikes include chalk, which fizzes in acid (it is carbonate), and volcanic ash or kaolin clay. The combination of extreme lightness, softness, high absorbency, and microscopic diatom shells is diagnostic.
Uses & significance
Diatomaceous earth is highly versatile. It is widely used as a filtration medium for water, beer, wine, and chemicals, exploiting its fine porosity. It serves as a mild abrasive in toothpaste and polishes, an absorbent for spills and pet litter, and a carrier for chemicals.
Food-grade DE is used as an anti-caking agent and a natural insecticide that dehydrates insects. Historically it stabilized nitroglycerin in dynamite. It also functions as a filler, an insulation material, and a soil amendment. Care should be taken to avoid inhaling the dust, especially crystalline silica forms.
Frequently asked questions
What is diatomaceous earth made of?
It is made of the fossilized silica shells (frustules) of diatoms, microscopic single-celled algae, forming hydrated amorphous silica.
What is diatomaceous earth used for?
It is used for filtration, as an absorbent, a mild abrasive, an anti-caking agent, a natural insecticide, and an insulation filler.
Is diatomaceous earth safe?
Food-grade DE is widely used safely, but its dust should not be inhaled, especially heat-treated forms containing crystalline silica.
How does diatomaceous earth kill insects?
Its fine silica particles abrade and absorb the waxy coating on insects, causing them to dehydrate and die.
Is diatomaceous earth the same as diatomite?
Yes. Diatomite is the rock and diatomaceous earth is essentially the same material, often referring to the processed or powdered form.
Diatomaceous Earth guides
In-depth guides for identifying, valuing, and understanding Diatomaceous Earth.
