Mineral & Geology

Imerys Kaolin is the world’s largest producer of quality kaolin and has deposits and production plants in the UK, USA, France, Belgium, Sweden and Brazil. Our products offer unique and specific geological characteristics that can be tailor-made to meet the changing demands of the markets that we serve.

In order to guarantee a long-term supply for its customers and secure its future growth, Imerys Kaolin aims to constantly have at least 20 years of reserves for all its minerals. To achieve this, the Group is constantly prospecting, optimizing its portfolio of deposits and acquiring new resources.


Kaolin (china clay) is a hydrated aluminium silicate crystalline mineral (kaolinite) formed over many millions of years by the hydrothermal decomposition of granite rocks. Hydrous kaolin is characterised by its fine particle size, plate like or lamellar particle shape and chemical inertness.

Kaolin is named after the hill in China (Kao-Ling) where it was first mined, for many years before it’s discovery in Europe (Cornwall, England) in 1745 by William Cookworthy who was looking for a source of material to produce white chinawares.

Markets for Kaolin

Kaolin is now used in the ceramics, paper, paint, plastics, rubber, sealant, adhesive and chemicals industries.

Formulated into Paint, fine kaolin such as Supreme™ can act as a functional extender of TiO2, reducing formulation cost and improving rheology. Coarser kaolins, Polwhite™ B & Polwhite™ E do not offer so much potential to extend TiO2 but do enhance the dry film properties of primers and undercoats. Polsperse™ 10 offers paint makers the possibility to extend TiO2 in solvent based gloss paints processed using high speed dissolvers rather than bead mills traditionally associated with this type of paint – cutting processing time and increasing efficiency.

Rubber formulations benefit from the use of fine kaolin, Supreme™ and Speswhite™, give semi-reinforcing properties and good barrier properties, particularly useful in automotive hose applications. The coarser kaolin, Polwhite™ E, can be used in flooring compounds to increase abrasion resistance as well as making the compound cheaper.

In sealants and adhesives, kaolin is used to modify rheological properties.

The Ultramarine Blue industry uses kaolin as a raw material for the synthesis of this important pigment, which is itself widely used in the Performance Minerals industries.

IMERYS is the world’s largest producer of quality kaolin and has deposits and production plants in the UK, USA, Australia and Brazil. Such a wide range of quality kaolin reserves is unique.

Quick View

Mineralogy: Kaolinite with minor amounts of mica, quartz and feldspar or illmenite

Particle Shape: Platy, with typical aspect ratio of 20:1

Specific Gravity: 2.6

Refractive Index: 1.56

MOH Hardness: 2.5

Moisture: (max %) 1.5

pH: 5-7.5


Calcined Kaolin is an anhydrous aluminium silicate produced by heating ultrafine natural kaolin to high temperatures in a kiln. The calcination process increases whiteness and hardness, improves electrical properties, and alters the size and shape of the kaolin particles.


Calcination occurs in two steps.

At 700°C the dehydroxylation of the kaolin is complete forming a poorly crystalline metakaolin. Products produced at this temperature include PoleStar™ 450  which can improve the dielectric properties of PVC cable insulation, and MetaStar™  which acts as a pozzolanic concrete additive.

At 980°C an amorphous defect spinel is formed which undergoes a transformation, with mullite recrystallising in an amorphous glass at temperatures above 1100°C. Products produced within this temperature range provide excellent properties in rubber compounds, especially when coated with silane, improving mechanical properties and chemical resistance. Silane treatment further enhances rigidity, toughness and dimensional stability in polyamide mouldings.

Markets for Calcined Kaolin

When formulated into film compounds Imerys calcined kaolin improves the thermal properties of agricultural films, giving the potential to reduce heating costs, reduce the planting to cropping time and increase the length of the growing season. In film that requires antiblock additive, calcined kaolin offers an ideal and cost effective balance of antiblock, haze and clarity performance.

In plastics the use of calcined kaolin is in PVC cable to improve electrical performance and in it’s coated form as Polarite 102A, as a functional filler in engineering thermoplastics.

PoleStar™ 200P is a very effective opacifying extender in paint, partially replacing TiO2, reducing the overall cost of paint formulations but maintaining paint film quality.

IMERYS offers a range of high performance calcined kaolins from its production plants in the UK and USA.

Quick View

Mineralogy: Metakaolin or amorphous, aluminium silicate (defect spinel)

Particle Shape:  Irregular, with surface voids

Specific Gravity:          2.6

Refractive Index:          1.56

MOH Hardness:              4-5

Moisture: (max %)          0.5

pH:         6-8

Product Spotlight


Supreme™ premium kaolin from IMERYS gives multiple benefits when used in decorative matt wall paints, functioning both as an opacifying extender and also as a rheology modifier.
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