What is Diatomite?
Diatomite, also known as diatomaceous earth, is a soft, friable, and light-colored sedimentary rock composed mainly of the fossilized remains of diatoms—microscopic, single-celled algae with silica-based cell walls.
Stan Celestian
These remains accumulate over millions of years in marine or freshwater environments and are eventually compacted into diatomite. Due to its high porosity, fine particle size, and low specific gravity, diatomite is used in a variety of industries as a filter media, absorbent, and lightweight filler for products like paint, plastics, and rubber. When crushed into a fine powder, diatomite is typically called “diatomaceous earth” (D.E.).
What are Diatoms?
Diatoms are a large group of algae that thrive in oceans, lakes, and even soils. Most diatoms are microscopic, but some species can grow up to two millimeters in length. These organisms are photosynthetic, producing nearly half of the organic matter in the world’s oceans.
Diatoms are unique in that they produce silica-based cell walls, known as frustules, which are intricately structured and highly porous. These features make diatoms excellent for filtering applications, as their frustules trap tiny particles from liquids.
When diatoms die, their siliceous frustules sink to the bottom of water bodies. In areas where the sediment is composed of over 30% diatom frustules by weight, it is known as diatom ooze or siliceous ooze. Over time, these sediments are lithified into diatomite.
Physical Properties of Diatomite
Diatomite is typically white to off-white in color, with a chalky texture and extremely low density. It is known for being porous and lightweight, which contributes to its high surface area and makes it ideal for industrial applications such as filtration and absorbency.
Physical Characteristics:
- Chemical Classification: Siliceous sedimentary rock
- Color: White, off-white, gray
- Streak: White
- Luster: Dull to earthy
- Diaphaneity: Opaque
- Cleavage: None
- Fracture: Conchoidal to uneven
- Mohs Hardness: 1-1.5
- Specific Gravity: 0.6 to 0.9 (extremely low density)
- Diagnostic Properties: Lightweight, porous texture, and fine particle size
- Chemical Composition: Primarily silica (SiO₂), often containing clay, iron oxides, and organic material
- Crystal System: Amorphous
Formation and Geological Occurrence of Diatomite
Diatomite forms in marine and freshwater environments, where diatoms flourish. Upon their death, their silica-based skeletons accumulate on the sea or lake floors. Over time, these sediments become compacted, forming diatomite. Deposits of diatomite are typically found in areas that were once ancient lakes or seas.
Some of the most important diatomite deposits are found in sedimentary environments, where phosphatic organic material (bones, teeth, scales) accumulated and was mineralized over time. Diatomite also occasionally forms as well-formed hexagonal crystals in hydrothermal veins and pegmatite pockets, but these occurrences are rare. The largest deposits of diatomite today are mined in places like California, Nevada, and Oregon in the United States, as well as China, Denmark, and Mexico.
Freshwater vs Saltwater Diatomite
Diatomite is found in both freshwater and marine environments, but the distinction between the two is critical for certain uses. Freshwater diatomite is preferred for products that come into contact with humans, animals, or plants because it lacks the salts found in marine diatomite, which can cause harmful or toxic effects. Marine diatomite, on the other hand, may contain impurities like salt, making it less suitable for some applications.
Uses of Diatomite and Diatomaceous Earth
Diatomite’s porous and lightweight properties make it highly useful across many industries. In 2017, diatomite consumption in the United States was divided into four primary categories: filtration (50%), light aggregate (30%), fillers (15%), and absorbents (5%). These uses take advantage of diatomite’s:
- Small particle size
- High porosity
- High surface area
- Relatively inert siliceous composition
- Low specific gravity
Filter Media
The intricate structure of diatom frustules makes diatomite an ideal filter media. The pores within and between frustules are small enough to trap bacteria, clay particles, and suspended solids. Diatomaceous earth is used as a filtration aid in water treatment plants, swimming pools, and the production of beer, wine, juices, and syrups.
Cement Additive
Diatomite is commonly added to Portland cement to boost its silica content, which improves the strength and durability of the final product. High-quality diatomite contains over 80% silica, and it is mixed with other raw materials like limestone and shale during cement production.
Filler
Diatomite is used as an inert, lightweight filler in products like paint, plastics, and asphalt shingles. It enhances the texture and reduces the overall weight of the product while providing additional functionality, such as improving adhesion resistance in rubber products.
Absorbent
Due to its high porosity, diatomaceous earth can absorb an amount of liquid equivalent to its own weight. This property makes it useful for cleaning up spills of oil and chemicals, and it is used as an ingredient in kitty litter and soil conditioners.
Mild Abrasive
Diatomaceous earth is used as a mild abrasive in products like toothpaste, facial scrubs, and metal polishes. Its small, angular silica particles make it effective at polishing without being too harsh on delicate surfaces.
Insect and Slug Control
Diatomaceous earth is used as a natural insecticide in gardening and pest control. Its sharp particles damage the exoskeletons of insects, causing them to dehydrate. It is effective against ants, fleas, roaches, and slugs, and is often used in organic farming.
Hydroponic Gardening
Diatomaceous earth is sometimes used as a growing medium in hydroponic gardens due to its ability to hold water while allowing the soil to breathe, promoting healthy root growth.
Leading Diatomite Producers
In 2017, 29 countries produced commercial quantities of diatomite. The United States led production with over 700,000 metric tons, followed by countries like Czechia, Denmark, China, and Argentina, each producing over 400,000 metric tons. Other notable producers include Mexico, France, Japan, Russia, South Korea, and Turkey.
Gemology
Diatomite is not typically used in jewelry due to its fragility and low hardness, but it holds significant geological interest. Under a microscope, the fossilized diatoms within diatomite display intricate patterns, making it an important tool for studying ancient ecosystems and paleoenvironments.
Fun Facts
- Biological Origin: Diatomite is composed of the fossilized remains of diatoms, which are responsible for producing nearly half of the organic mass in the world’s oceans.
- Lightweight and Porous: Some forms of diatomite are so lightweight that they can float on water until they become saturated.
- Insect Control: Diatomaceous earth is a natural insecticide, used widely in organic farming and pest control.
Diatomite is an extraordinary material with a wide range of uses, from filtration to pest control and abrasives. Its formation from fossilized algae provides insight into Earth’s geological past, while its versatile properties continue to make it a critical resource in modern industries.
