Actinolite

Actinolite is an amphibole mineral containing calcium, magnesium and iron, and it forms a series with tremolite. Because of its iron it is darker and brighter green than tremolite, and it forms ray-like or bladed, sometimes fibrous crystals. Its name comes from the Greek aktis, “ray”. Its finely interlocked fibres make nephrite jade, and its variety that reflects light in a band gives the “cat's-eye” stone; its splittable fibrous form is counted as asbestos and is dangerous.

Jade (nephrite): Nephrite, formed by the interlocking of fine actinolite and tremolite fibres, is one of the two kinds of jade (see the Jade page). Cat's-eye: Translucent to opaque green actinolite that reflects light in a band (chatoyancy) is cut as cabochons and used as an ornamental stone. Collecting: Green, ray-like bundles of crystals find a place in mineral collections. As asbestos: Its fibrous form was formerly mined as asbestos; today this use is banned or restricted because of the health risk.

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 3.03–3.24 g/cm³.

Its best-known localities: Gundagai (Jones Creek area), New South Wales, Australia; Mount Greiner, Zillertal, Tyrol, Austria; Zermatt, Valais, Switzerland; Arendal, Agder, Norway; Mogok, Mandalay Region, Myanmar.

Known localities in Türkiye: Camiboğazı skarn deposit, Gümüşhane, Türkiye.

Bundles of long bladed or ray-like crystals, from pale to dark and greyish green; darker than tremolite. Its hardness is 5–6: a steel knife scratches it only with difficulty. It has good cleavage in two directions; a broken crystal shows surfaces meeting at about 56° and 124°. It is found in low-grade metamorphic rocks together with chlorite, epidote, talc and albite, and can accompany glaucophane in blueschists. Fibrous actinolite can be confused with tremolite and other types of asbestos; only a laboratory can say which it is. All are classed as carcinogenic.

On the “street to diamond” value ladder it sits on step 2 of nine: Raw material by the tonne. Actinolite is a very common mineral and is often worthless. As an ornamental stone its value depends on colour and toughness in nephrite jade, and in cat's-eye stone on how sharp the band of reflected light is, on translucency and on the quality of the cut. Collectors look for long, well-formed, undamaged bundles of crystals; fibrous (asbestos) specimens are not recommended because of the health risk.

Today crystal-therapy sources present actinolite as a powerful “protection stone”, claiming that it bandages the “wounds” left by illness and stress and shields people from negative influences. The same sources link actinolite with the heart chakra and say that it deepens calm in meditation, emotional balance and compassion. None of these claims can be measured or tested. The really notable thing about actinolite is that its fibrous form is asbestos: so the stone should not be ground to powder, no stone water or elixir should be made from it, and the dust from cutting it must not be inhaled. For illness or stress, seek medical support. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

When actinolite is fibrous (asbestos) it is, like other types of asbestos, carcinogenic to humans (IARC Group 1). When airborne fibres are inhaled they can cause lung cancer, mesothelioma and asbestosis, often only decades later. Do not break, cut or sand rocks of fine, silky fibrous actinolite and do not breathe their dust; do not grind the stone to drink it and do not make stone water. Collection specimens should be kept in a sealed, labelled container. In Türkiye the production, placing on the market and use of asbestos and asbestos-containing products has been banned since 31 December 2010.