The facts
What diatomite actually is
Mineralogically, diatomite is a sedimentary rock composed of the opaline silica frustules of fossil diatoms - a biogenic silica with extraordinary porosity — Amorphous opaline silica SiO2.nH2O, typically 80-90%, with clay and volcanic ash, crystallising in the amorphous system.
The colour is caused by white to cream; darker where organic matter or clay is present. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.42-1.48 (opal-A), and the specific gravity sits near 1.90-2.35 true density; bulk density 0.10-0.35 - it is extraordinarily light; cleavage is none.
Where diatomite comes from
The recognised sources are Lompoc, Santa Barbara County, California, USA - the largest and highest-quality deposit, Fernley and Storey County, Nevada, USA, Mors and Fur, Limfjord, Denmark (moler, a diatomite-clay), Murat and Auvergne, France; Alicante and Murcia, Spain and Mexico, Peru and China.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How diatomite is treated
Dried, milled, and for filtration grades CALCINED or flux-calcined with soda ash. THIS IS THE CRITICAL HEALTH POINT: natural uncalcined diatomite is amorphous silica with low toxicity, but calcining converts much of it to CRISTOBALITE, a crystalline silica and a Group 1 carcinogen - filter-aid grades can contain 40-70% cristobalite and require respiratory protection. 'Food grade' DE sold for garden and pest use is the uncalcined form. Uses: beer, wine and swimming-pool filtration, fillers, insulation, absorbents, and mechanical insecticide.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What diatomite is confused with
The usual confusions are Perlite (the other major filter aid), Talc and kaolin as fillers, Pumice and Synthetic silica.
The separation is rarely a matter of opinion: refractive index 1.42-1.48 (opal-A) and specific gravity 1.90-2.35 true density; bulk density 0.10-0.35 - it is extraordinarily light settle most of it in a minute, and magnification settles the rest.
What diatomite is used for
Diatomite is bought by filtration, heavy industry, abrasives, cosmetics and kitchen and table — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the tonne or by the piece.
Durability and care
Diatomite is 1-2 as a rock (the individual silica frustules are harder, around 4.5-5) on the Mohs scale, with none cleavage.
Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What diatomite costs
Indicative pricing for diatomite is $250-600 per tonne depending on grade; US average unit value is in the upper part of that range, and specialty filter aids exceed it.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is diatomite treated, and how?
Dried, milled, and for filtration grades CALCINED or flux-calcined with soda ash. THIS IS THE CRITICAL HEALTH POINT: natural uncalcined diatomite is amorphous silica with low toxicity, but calcining converts much of it to CRISTOBALITE, a crystalline silica and a Group 1 carcinogen - filter-aid grades can contain 40-70% cristobalite and require respiratory protection. 'Food grade' DE sold for garden and pest use is the uncalcined form. Uses: beer, wine and swimming-pool filtration, fillers, insulation, absorbents, and mechanical insecticide.
Where does diatomite come from?
Lompoc, Santa Barbara County, California, USA - the largest and highest-quality deposit, Fernley and Storey County, Nevada, USA, Mors and Fur, Limfjord, Denmark (moler, a diatomite-clay), Murat and Auvergne, France; Alicante and Murcia, Spain and Mexico, Peru and China. Origin affects price, so we name the locality rather than the country on every quote.
Is diatomite hard enough to wear every day?
Not really. At 1-2 as a rock (the individual silica frustules are harder, around 4.5-5) on the Mohs scale it is softer than the quartz dust in ordinary household dirt, so it scratches with wear. It suits pendants, earrings and objects better than a daily ring.
How much does diatomite cost?
Indicatively $250-600 per tonne depending on grade; US average unit value is in the upper part of that range, and specialty filter aids exceed it. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is diatomite confused with?
Most often Perlite (the other major filter aid), Talc and kaolin as fillers, Pumice and Synthetic silica. A refractive index of 1.42-1.48 (opal-A) and a specific gravity near 1.90-2.35 true density; bulk density 0.10-0.35 - it is extraordinarily light separate it quickly.
What is diatomite used for besides jewellery?
filtration, heavy industry, abrasives, cosmetics and kitchen and table. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for diatomite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about diatomite