Scientific Association of the European Talc Industry aisbl

Mr. John Addison BSc, F Min Soc, Consultant Mineralogist specialising in the identification and analysis of asbestos and industrial minerals, their toxicity and effects on human health, has accepted to reply to this question.

Asbestiform is a term that is used to describe the mineral habit of minerals that are formed in a fibrous state that resembles asbestos. The American Society for Testing Materials (ASTM) has defined asbestiform minerals as mineral fibre populations generally having the following characteristics when viewed by light microscopy: (1) many particles with aspect ratios ranging from 20:1 to 100:1 or higher (greater than 5µm in length); (2) very thin fibrils generally less than 0.5µm in width; and (3) in addition to the mandatory fibrillar crystal growth, two or more of the following attributes: (a) parallel fibres occurring in bundles, (b) fibres displaying splayed ends, (c) matted masses of individual fibres, and (d) fibres showing curvature.

The common asbestos minerals fit this description perfectly, but in addition they are characterised by having high tensile strength and pronounced durability.

A number of other minerals including gypsum, calcite, brucite and talc can, rarely, occur in a fibrous habit that can be described as asbestiform. The use of the term is accurate in that the minerals in this unusual habit do resemble asbestos, but they do not have the other physical and chemical properties of asbestos. In particular they do not have any of the toxicological properties of asbestos.

In the case of talc, this mineral habit is rare and there are few proven occurrences of talc in this form. Asbestiform talc in this sense is encountered as a geological curiosity, mostly in the mineralogical collections of enthusiasts, and has no significant public health risk implications.

Certain other materials have also been referred to as `asbestiform talc'. A small number of talc deposits, mostly in the eastern parts of the USA, have been found to contain unusual minerals that appear to consist of intimate mixtures of talc and anthophyllite, or talc and tremolite. These mixtures of talc and amphibole were first recorded in the 1980s and are sometimes called talcboles, referring to the fact that, even in single small crystals, the crystal lattice appears to be an inter-lamination of talc and amphibole structures. These crystals can form or separate into long thin fibres that are very similar to asbestos in appearance. These fibres are not asbestos, and there is little evidence to show that they have the same toxicological properties as asbestos. None of these unusual minerals have been found in other talc deposits around the world.
Finally, the term `asbestiform talc' has also been applied recently to talc containing asbestos. This is a misuse of the term since `asbestiform' can only ever be used to describe a mineral habit. The correct term for this mixture is simply talc containing asbestos. Thanks to high standards of quality control and selective mining methods where necessary, the commercial talcs supplied by EUROTALC Members do not contain asbestos as defined by the European directive 83/477/EEC, when analysed by conventional methods. This statement is based upon verification by certified independent laboratories.

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