Diatomite Rock Type, Composition, Formation, Occurrence

Diatomite Rock
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Diatomite is a chalk-like, friable, soft, earthy, and fine-grained siliceous sedimentary rock. The rock is also called diatomaceous earth. It usually has a light color (white to gray, rarely black). The colors are usually added due to impurities in the rock.

Diatomite has a particle size ranging from more than 1 μm to less than 1 mm. The rock is often abrasive, depending on its granularity. It is crushed to make a fine white to off-white powder. Its powdered form often feels like pumice powder with low density due to high porosity.


Rock Discovery

Diatomite was discovered in the 1830s by a German peasant Peter Kasten. The rock is known as “Kieselgur” in the German language. He discovered the rock while sinking a well on the northern slopes of the  Haußelberg hill in North Germany.

Rock Composition

The rock has a high silica content, usually 80-90%. The rock has 2-4% alumina content (clay minerals) and 0.5-2% iron oxide.

An interesting fact about diatomite’s composition is that each reserve is different. The amount of silica combined with natural clays and minerals. The silica content varies depending on the sedimentation conditions, presence or absence and concentration of other sediments (sand, clay, and volcanic ashes), and the deposits’ old. The diatom species may also differ from one reserve to another.

Diatomite is known as diatomaceous earth when it is in crushed form
Diatomite is known as diatomaceous earth when it is in crushed form

Diatomite Formation

Diatomite is formed in a marine environment (lake or marine sediment) by silica remains of dead diatoms. Diatoms are microscopic single-celled algae. These organisms leave behind shells that provide the silica diatomites are composed of.

Marine diatomites are associated with various other rock types, but lacustrine diatomites are almost always associated with volcanic rock. Diatomaceous chert is made up of diatomite cemented or bound with silica.

Scanning electron micrograph of diatomaceous earth
Scanning electron micrograph of diatomaceous earth

Saltwater vs. Freshwater Diatomite

Diatomite can grow in seawater and freshwater environments. The origin is an important factor when considering how to use the rock. Saltwater diatomite has a high salt concentration. Hence, it must not be used in any application that involves humans, plants, and animals.

Where is Diatomite Found?

Diatomite is a relatively uncommon rock. The leading producers are the USA, Czech, Denmark, and China. Other countries that produce commercial quantities of the rock are France, Russia, South Korea, Turkey, Spain, Mexico, Peru, Argentina, and Japan.

Deposits in Colorado and Nevada, United States, are up to several hundred meters thick and stretch for miles. The world’s largest diatomite deposits are in Santa Barbara County, California.

Diatomite Uses

Diatomite is commercially available in several forms. It is used in granulated form, small particles (micronized form ranging from 10 μm to 50 μm) to be used as an insecticide, and calcined form is heat-treated and activated for filters.

Diatomite is used as a filter, aggregate, filler, and absorbent. Diatomite has a small particle size, high porosity and surface area, inert siliceous composition, and low specific gravity.

Its main uses are briefly explained below.

Filtration Media: Diatomite has a small particle size and an open structure that allows it to filter particles, bacteria, sand, debris, and other suspended particles. Common filtration applications include drinking water systems, swimming pool filters, breweries, and chemical plants.

Filler: Diatomaceous earth is a lightweight and inert filler in many applications. Common examples include whitening agents in paints, plastics, and asphalt shingles and improving adhesion resistance in rubber products.

Cement Additive: High-quality diatomite contains over 80% silica. It is used as an additive in cement. It is crushed and mixed with limestone and shale to make cement.

Absorbent: Diatomite quickly absorbs liquid. When placed over liquid spills, it can absorb and hold liquids equivalent to its weight. These properties facilitate cleanup and removal. It is often used in cosmetics and facial masks to absorb skin oils.

Gardening: It is used in place of soil in hydroponic gardens and farming. Hydroponic farming refers to growing plants without using soil. It can hold the water required for plants to grow.

Mild Abrasive: The rock is also used as a mild abrasive in some kinds of toothpaste, facial scrubs, and metal polishes. The silica particles in the rock are small, crispy, angular in shape, and have a high surface area.

Insecticide: Diatomite is absorbent and abrasive. These properties make it an effective insecticide. It can prevent ants, fleas, lice, roaches, mites, and ticks growth inside.

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