Diatomite, also known as diatomaceous earth, is a soft sedimentary rock composed of the fossilized remains of microscopic algae called diatoms. This naturally occurring substance is a fine, white or off-white powder found in deposits across the globe. The material is used in thousands of products and industrial processes, valued for a unique combination of properties derived from its microscopic origins.
Geological Formation and Chemical Makeup
Diatomite’s formation unfolds over millions of years from diatoms, a group of algae that inhabit both freshwater and saltwater environments. These organisms construct hard shells for themselves by absorbing water-soluble silica. When the diatoms die, their organic parts decompose, but their durable, silica-based skeletons sink and accumulate at the bottom of lakes and oceans. Over geological time, these layers of fossilized remains build up and are preserved as diatomite deposits.
The chemical composition of diatomite is primarily silicon dioxide (SiO₂). In diatomite, the silica is amorphous, meaning its atoms lack a defined, crystalline structure. This is a direct result of the biological process by which diatoms form their shells. Most diatomite contains other minerals and clays as impurities, which can affect its properties and suitability for certain applications. The origin of the deposit, whether from freshwater or saltwater, also influences its characteristics and potential uses.
Distinctive Physical and Chemical Properties
The utility of diatomite stems from its physical characteristics. Its primary trait is high porosity, inherited from the hollow structures of the individual diatom fossils. This structure results in a very low density, making the material lightweight, and an exceptionally large surface area. These microscopic voids make diatomite a highly effective absorbent material.
Diatomite is also chemically inert, meaning it does not readily react with other substances. This stability makes it a reliable component in industrial processes. The material possesses a naturally abrasive texture, similar to pumice powder, due to the hardness of the silica particles. Its structure also gives it thermal insulating properties, allowing it to act as a barrier against heat.
Widespread Uses Across Industries
One of the most significant applications of diatomite is in filtration. Its network of pores is suited for trapping microscopic impurities from liquids. This property is used in the food and beverage industry to clarify products like beer, wine, and fruit juices. It is also used to filter water in swimming pools and in the manufacturing of pharmaceuticals.
The absorbent nature of diatomite makes it useful for cleaning up spills in industrial and automotive settings and as an ingredient in products like cat litter. Other common uses include:
- As a filler material to add bulk and strength to paints, plastics, rubber, and paper.
- As a mild abrasive in cosmetics and personal care products like toothpaste and facial scrubs.
- As a non-chemical insecticide that damages the waxy outer layer of insects, causing them to dehydrate and die.
- As a soil amendment to improve water retention, drainage, and aeration in gardens.
- As an anti-caking agent in animal feed to prevent clumping.
Grades of Diatomite and Safe Handling
Diatomite is processed into different grades for specific applications, primarily natural-grade and calcined-grade. Natural diatomite is crushed, dried, and milled, is very low in crystalline silica, and is often called “food-grade.” This is the type used in agriculture, as a feed additive, and in some dietary supplements.
Calcined grades are produced by heating raw diatomite to high temperatures, sometimes with a fluxing agent. This process, known as calcination, removes impurities and alters the physical structure, making it more effective for filtration. However, the high heat converts a significant portion of the amorphous silica into a crystalline form.
This distinction is important for safety. While amorphous silica is considered safe, the inhalation of fine crystalline silica dust can pose a health risk, leading to a lung disease called silicosis. For this reason, industrial-grade calcined diatomite, such as that used for pool filters, is not suitable for consumption or agricultural use. When handling any diatomite powder, take precautions to minimize dust inhalation by using proper ventilation or respiratory protection.