Diatomaceous earth can come from freshwater lakes or marine environments, but does the source make a meaningful difference?
Both freshwater and marine diatomaceous earth are formed from the fossilised remains of microscopic aquatic organisms called diatoms. However, the species of diatoms, surrounding geology, mineral content and processing methods can vary considerably between deposits.
These factors influence the physical properties, purity, silica profile and intended use of the finished product. Importantly, freshwater diatomaceous earth is not automatically food grade, and marine diatomaceous earth is not automatically pool grade.
Soil Solutions supplies Perma-Guard Food Grade Diatomaceous Earth, also known as Fossil Shell Flour. It is sourced from a freshwater deposit and is predominantly composed of amorphous silica.
To understand the benefits and what makes one diatomaceous earth product different from another, it helps to look beyond the words “freshwater” and “marine”.
How Do Diatomaceous Earth Deposits Form?
Diatoms are microscopic, single-celled organisms found in freshwater and marine environments. They develop porous external structures called frustules, which are primarily made from silica.
When diatoms die, their microscopic shells can settle on the bottom of lakes, rivers, streams, coastal basins or oceans. Over millions of years, large quantities of these silica-rich remains may accumulate and form deposits of diatomite—the naturally occurring sedimentary material from which diatomaceous earth is produced.
The United States Geological Survey explains that commercially valuable freshwater deposits are commonly associated with ancient lake systems, while marine deposits often developed along continental margins where nutrient-rich water supported large diatom populations.
These deposits are mined and processed into different grades for uses including:
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Absorbent products
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Agricultural and animal-feed applications
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Garden and household soil products
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Industrial filtration
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Fillers in manufactured products
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Mild abrasives
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Insulation and construction materials
A deposit’s aquatic origin is only one factor in determining which applications the finished material may suit.
What Is Freshwater Diatomaceous Earth?
Freshwater diatomaceous earth is obtained from deposits that developed in ancient lakes and other freshwater environments.
The conditions within a lake can influence which diatom species were present and which other materials accumulated alongside them. Freshwater deposits can contain clay, volcanic material, iron compounds, sand and other naturally occurring minerals.
Some freshwater deposits contain well-preserved diatom structures and a high proportion of amorphous silica. Others may contain more impurities or have physical properties that make them better suited to industrial uses.
This means the term “freshwater diatomaceous earth” does not provide enough information on its own to determine:
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Whether it is food grade
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Its amorphous and crystalline silica content
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Its purity
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How it has been processed
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Whether it is suitable for soil in gardens, animals or household areas
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Whether it has been assessed for a particular application
The deposit must be evaluated, processed and classified according to the intended finished product.
Perma-Guard Fossil Shell Flour is produced from a freshwater deposit formed during the Miocene epoch. The manufacturer describes the deposit as containing preserved tubular diatom structures and predominantly amorphous silica.
You can read more about its documented characteristics in What Makes Perma-Guard Diatomaceous Earth Different?.
What Is Marine Diatomaceous Earth?
Marine diatomaceous earth, sometimes informally called saltwater diatomaceous earth, comes from diatoms that accumulated in oceans, coastal basins and other saltwater environments.
“Marine” is the more accurate professional term because these deposits are associated with marine geological environments rather than simply water containing salt.
Marine deposits can be extremely large and commercially valuable. According to the United States Geological Survey, marine deposits generally cover larger areas and may be thicker than many freshwater deposits. High-quality marine diatomite is widely used in filtration and other industrial applications.
As with freshwater deposits, marine diatomaceous earth can vary in:
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Diatom species and structure
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Silica content
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Particle size
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Porosity
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Mineral composition
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Organic material
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Naturally occurring contaminants
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Processing requirements
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Intended end use
Marine origin does not automatically mean the material is inferior, highly crystalline or unsuitable for non-industrial applications. The specific deposit and how it is processed are more informative than the marine label alone.
Do Freshwater and Marine Diatoms Have Different Structures?
Thousands of diatom species exist, and their microscopic shells occur in many different shapes and sizes.
Depending on the species, a diatom may have a round, elongated, tubular, cylindrical or boat-like structure. It may contain pores, ridges and other microscopic features that affect its surface area and physical behaviour.
Freshwater and marine environments support different combinations of diatom species. However, there is no single structure shared by every freshwater diatom or every marine diatom.
Even two freshwater deposits can have different dominant species and physical characteristics. The same applies to two marine deposits.
Consequently, statements such as “all freshwater diatoms are tubular” or “marine diatoms are always fragile” are too broad. Buyers should look for information about the particular deposit and finished product rather than relying on a general comparison between aquatic environments.
Deposit Composition Matters
A natural diatomite deposit rarely consists exclusively of fossilised diatom shells. It may also contain minerals and sediments introduced by the surrounding geological soil and environmental conditions.
These can include:
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Clay
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Sand
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Volcanic ash
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Iron oxides
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Calcium compounds
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Other forms of silica
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Organic matter
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Trace minerals
The colour of diatomaceous earth may provide some indication of its mineral composition, but colour alone does not prove purity, grade or suitability.
A white or light-coloured product is not automatically food grade, just as a darker product is not necessarily poor quality. Reliable product specifications, mineral analysis and safety documentation provide more useful information.
Particle size and the preservation of the diatom structures also matter. Milling a product too aggressively may break down some of its microscopic structure, while insufficient processing may leave unwanted material in the finished powder.
Processing Can Be More Important Than the Source
After extraction, raw diatomite can undergo several processing steps. Depending on the intended product, these may include:
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Crushing the mined material
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Drying it to remove moisture
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Removing unwanted material
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Milling it to a specified particle size
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Separating or classifying the particles
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Heating or calcining it for particular industrial applications
Some diatomaceous earth is sold in a relatively natural, uncalcined form after drying and milling. Other products are heated to high temperatures to alter their physical characteristics.
Calcination can improve the material’s performance for filtration by changing its particle structure and flow properties. However, high-temperature processing can also convert some amorphous silica into crystalline silica, particularly cristobalite.
This is one reason pool-filter diatomaceous earth and food-grade diatomaceous earth should never be treated as interchangeable products.
For a fuller explanation, read Food-Grade vs Pool-Grade Diatomaceous Earth: What’s the Difference?.
Amorphous vs Crystalline Silica
Silica occurs in both amorphous and crystalline forms. The difference relates to the way its molecular structure is arranged.
Most naturally occurring, uncalcined diatomaceous earth consists predominantly of amorphous silica. However, it may also contain a small amount of naturally occurring crystalline silica.
High-temperature processing can increase the crystalline silica content of certain diatomaceous earth products. This is particularly relevant to some filter-grade products that have been calcined or flux-calcined.
Crystalline silica presents a serious inhalation hazard when sufficiently fine particles become airborne and are breathed into the lungs. Although amorphous silica has a different risk profile, any fine diatomaceous earth powder should still be handled carefully.
Avoid creating airborne dust, avoid breathing the powder and follow the product’s label and safety information. Appropriate respiratory and eye protection may be required when handling larger quantities or when dust could become airborne.
“Food grade” describes a product specification and intended application. It does not mean the fine powder is safe to inhale.
Is Freshwater Diatomaceous Earth Better Than Marine DE?
Neither freshwater nor marine diatomaceous earth is universally better.
The appropriate choice depends on:
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The quality and consistency of the deposit
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The dominant diatom species
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The condition of the fossilised structures
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The proportion of amorphous and crystalline silica
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Other minerals and impurities present
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Particle size
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Processing method
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Product grade
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Supporting documentation
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The intended application
A high-quality marine deposit may be ideal for filtration, while a carefully selected and processed freshwater deposit may suit food, feed, garden or absorbent applications.
Conversely, not every freshwater deposit will meet food-grade specifications, and not every marine product has been calcined for pool filtration.
A product should be judged by its documented characteristics—not by the freshwater or marine description alone.
What Should Customers Check Before Buying DE?
Before purchasing diatomaceous earth, check the following information.
1. Product grade
Confirm whether it is food grade, feed grade, pest-control grade, industrial grade or pool-filter grade. Never assume these products are interchangeable.
2. Intended applications
Read the product label to determine where and how it may be used. Choose a product specifically suited to your intended application.
3. Processing method
Find out whether the material is natural or uncalcined, calcined, or flux-calcined. Processing can significantly alter its properties.
4. Silica profile
Look for available information about amorphous and crystalline silica content rather than relying on the product’s source or colour.
5. Product documentation
Check for a current label, safety data sheet, mineral analysis and manufacturer specifications.
6. Source and manufacturer
Choose a traceable product from a supplier that clearly identifies the manufacturer and provides practical handling information.
7. Safety directions
All fine mineral powders require careful handling. Minimise dust, avoid inhalation and eye contact, store the product securely and follow the supplied directions.
Choosing Diatomaceous Earth for Your Pest Control
The difference between freshwater and marine diatomaceous earth begins with the environment in which the original diatoms lived. However, that is only the beginning of the comparison for pest management.
Freshwater diatomaceous earth can be well suited to pest control applications when it comes from a high-quality deposit containing well-preserved, porous diatom structures and predominantly amorphous silica.
These microscopic structures provide a large surface area that helps the dry powder remove oils and moisture from the protective outer layer of susceptible crawling insects. However, freshwater origin alone does not guarantee better performance against insects than marine diatomaceous earth. Effectiveness also depends on the deposit’s purity, diatom structure, particle size, processing method and how the product is applied.
Perma-Guard Fossil Shell Flour is sourced from a freshwater deposit selected for its preserved diatom structures and amorphous-silica profile, making it suitable for appropriate targeted pest control applications around plants when used according to the product directions.
The diatom species, surrounding geology, deposit composition, mining practices, particle size, processing method, silica profile and final product specifications all influence the material that reaches the customer.
Perma-Guard Fossil Shell Flour is a food-grade product sourced from a freshwater deposit and predominantly composed of amorphous silica. Soil Solutions supplies it in several sizes for appropriate garden, household and animal-environment applications.
View Perma-Guard Food Grade Diatomaceous Earth
Always choose the correct grade for the intended application and follow the manufacturer’s directions and safety information.
Frequently Asked Questions
Is freshwater diatomaceous earth always food grade?
No. Freshwater describes the environment in which the original diatoms lived. Food grade depends on the deposit’s composition, processing, finished-product specifications and applicable quality requirements.
Is marine diatomaceous earth the same as pool-grade DE?
No. Some marine diatomite is processed into filtration products, but marine origin alone does not make a product pool grade. Pool-grade DE is defined more meaningfully by its processing and intended use.
Can freshwater and marine DE contain crystalline silica?
Yes. Naturally occurring deposits may contain some crystalline silica. High-temperature calcination can also convert part of the amorphous silica into crystalline forms. Check the product documentation for the specific material.
Can pool-grade diatomaceous earth be used in gardens?
Pool-filter DE should not be substituted for food-grade or garden-appropriate DE. It is processed for filtration and can have a different silica profile and physical properties.
What is the best way to compare diatomaceous earth products?
Compare the product grade, intended use, processing method, silica profile, particle characteristics, manufacturer information and safety documentation. Do not make the decision solely on whether the deposit is freshwater or marine.