Tremolite

Tremolite is an amphibole (double-chain silicate) containing calcium and magnesium. It usually forms white, grey or pale green, long bladed crystals and fibrous or columnar masses. Its tough, massive form, made of finely interlocked fibres, is nephrite jade; its form that splits into silky fine fibres is asbestos. The asbestos in the “white soil” (“ak toprak”) once used to plaster and whitewash houses in some Turkish villages is mostly tremolite.

Jade (nephrite): Nephrite, the tough rock made of tightly interlocked tremolite–actinolite fibres, is one of the two kinds of jade; it is carved into figurines, jewellery and ornaments (see the Jade page). Collecting: Long bladed or wedge-shaped crystals and lavender-pink specimens find a place in mineral collections. As asbestos: Its fibrous form counts as asbestos, though most commercial asbestos was chrysotile. Today tremolite is less a raw material than a contaminant: fibrous tremolite can turn up in talc, vermiculite and chrysotile deposits.

It has a hardness of 5–6 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 2.99–3.03 g/cm³.

Its best-known localities: Campolungo, Piumogna Valley, Leventina, Ticino, Switzerland; Saint-Marcel, Aosta Valley, Italy; Gouverneur, St. Lawrence County, New York, USA; Franklin, Sussex County, New Jersey, USA; Wilberforce, Ontario, Canada.

Known localities in Türkiye: Güzelyurt, Hekimhan, Malatya, Türkiye; Camiboğazı skarn deposit, Gümüşhane, Türkiye.

It forms long, bladed or wedge-shaped crystals in white, grey or pale green, and also occurs in fibrous, columnar or granular masses. Some specimens run to lavender and pink. Its hardness is 5–6: a steel knife scratches it only with difficulty, and it cannot scratch quartz. It has two perfect cleavages; a broken crystal shows planes that meet at about 56° and 124°. It is found in dolomitic marbles and other rocks made from limestone, together with calcite, dolomite and diopside. Fibrous tremolite can be told from chrysotile (white asbestos) by its fibres: tremolite fibres are straight and stiff, chrysotile fibres are curly and flexible. This difference can only be seen reliably under a microscope; both are classed as carcinogenic in the same way.

On the “street to diamond” value ladder it sits on step 2 of nine: Raw material by the tonne. Tremolite is a very common rock-forming mineral and has almost no commercial value on its own. Collectors look for long, well-formed, undamaged crystals, especially from well-known localities such as the type locality, Campolungo. The value of nephrite worked as jade depends on its colour, toughness, translucency and origin. Fibrous (asbestos) specimens are not recommended even for collections because of the health risk.

The fibrous form of tremolite (tremolite asbestos) is, like all types of asbestos, carcinogenic to humans (IARC Group 1). When airborne fibres are inhaled they can cause lung cancer, mesothelioma (cancer of the lining of the lungs or abdomen) and asbestosis, often only decades later. Fibrous tremolite is also sometimes found as a contaminant in other materials such as talc, vermiculite and chrysotile. If you see fine, silky fibres in a rock, do not break, cut or sand it and do not breathe its dust; for suspect plaster, soil or building material, contact an accredited laboratory. Collection specimens should be kept in a sealed, labelled container and should not be handled or broken. In Türkiye the production, placing on the market and use of asbestos and asbestos-containing products has been banned since 31 December 2010.