The facts
What kaolin actually is
Mineralogically, kaolin is a clay rock dominated by kaolinite, formed by weathering or hydrothermal alteration of feldspar in granite and arkose — Kaolinite Al2Si2O5(OH)4, crystallising in the aggregate (triclinic kaolinite) system.
The colour is caused by white - and whiteness (ISO brightness) is the primary commercial grading criterion; iron and titanium impurities are what get removed. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.553-1.570, and the specific gravity sits near 2.16-2.68; cleavage is perfect basal.
Where kaolin comes from
The recognised sources are Sandersville and the Georgia kaolin belt, Georgia, USA - the world's premier paper-coating source, St Austell and Lee Moor, Cornwall and Devon, England (china clay), Rio Capim and Jari, Para, Brazil, Gaoling, Jingdezhen, Jiangxi, China - the village that gave the mineral its name and Zettlitz, Czech Republic; Ukraine.
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 kaolin is treated
Refined heavily: blunged, degritted, magnetically separated, chemically bleached, delaminated and sometimes calcined to metakaolin. Uses: paper filling and coating (historically the largest), ceramics and porcelain, refractories, paint and rubber filler, fibreglass, catalyst supports, and pharmaceuticals and cosmetics. Paper demand has declined with digitisation, shifting producers toward ceramics and performance fillers. Not hazardous, though respirable dust contains some crystalline silica from residual quartz.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What kaolin is confused with
The usual confusions are Ball clay (plastic, darker firing), Halloysite (tubular morphology, different applications), Talc and calcium carbonate as competing fillers and Bentonite.
The separation is rarely a matter of opinion: refractive index 1.553-1.570 and specific gravity 2.16-2.68 settle most of it in a minute, and magnification settles the rest.
What kaolin is used for
Kaolin is bought by heavy industry, cosmetics, kitchen and table and filtration — 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
Kaolin is 2-2.5 on the Mohs scale, with perfect basal 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 kaolin costs
Indicative pricing for kaolin is $80-200 per tonne for filler grades; premium coating, calcined and pharmaceutical grades $250-600 per tonne.
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 kaolin treated, and how?
Refined heavily: blunged, degritted, magnetically separated, chemically bleached, delaminated and sometimes calcined to metakaolin. Uses: paper filling and coating (historically the largest), ceramics and porcelain, refractories, paint and rubber filler, fibreglass, catalyst supports, and pharmaceuticals and cosmetics. Paper demand has declined with digitisation, shifting producers toward ceramics and performance fillers. Not hazardous, though respirable dust contains some crystalline silica from residual quartz.
Where does kaolin come from?
Sandersville and the Georgia kaolin belt, Georgia, USA - the world's premier paper-coating source, St Austell and Lee Moor, Cornwall and Devon, England (china clay), Rio Capim and Jari, Para, Brazil, Gaoling, Jingdezhen, Jiangxi, China - the village that gave the mineral its name and Zettlitz, Czech Republic; Ukraine. Origin affects price, so we name the locality rather than the country on every quote.
Is kaolin hard enough to wear every day?
Not really. At 2-2.5 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 kaolin cost?
Indicatively $80-200 per tonne for filler grades; premium coating, calcined and pharmaceutical grades $250-600 per tonne. 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 kaolin confused with?
Most often Ball clay (plastic, darker firing), Halloysite (tubular morphology, different applications), Talc and calcium carbonate as competing fillers and Bentonite. A refractive index of 1.553-1.570 and a specific gravity near 2.16-2.68 separate it quickly.
What is kaolin used for besides jewellery?
heavy industry, cosmetics, kitchen and table and filtration. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for kaolin?
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 kaolin