Fire opal

Fire opal is a transparent to translucent opal whose body colour runs from yellow through orange to red. The “fire” in the name describes the colour of the stone: most fire opal does not show the rainbow flashes of precious opal, though it occasionally gives off bright green flashes. Its most famous source is Mexico, but it also occurs in Türkiye, in the Simav area of Kütahya and around Gümüldür in İzmir.

Jewellery: being transparent or translucent, it can be cut as a cabochon (a polished dome) or as a faceted stone, and is used in rings, necklaces and earrings. Carving and ornaments: in Mexico the stone is cut and polished together with its host rock to make “cantera opal”. Collecting: bright, crack-free pieces are sought by mineral and gem collectors. Because fire opal contains water, it can crack with sudden changes in temperature and humidity; it should be stored with care and protected from knocks against hard surfaces.

It has a hardness of 5.5–6.5 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 1.9–2.3 g/cm³.

Its best-known localities: Ezequiel Montes–Tequisquiapan–Colón area, Querétaro, Mexico; Magdalena area, Jalisco, Mexico; Virgin Valley, Humboldt County, Nevada, USA; Wollo, Amhara Region, Ethiopia; Campos Borges, Rio Grande do Sul, Brazil.

Known localities in Türkiye: Simav–Şaphane area, Kütahya, Türkiye; Gümüldür area, Menderes, İzmir, Türkiye.

The body colour runs from yellow through orange to red, sometimes brown; the stone is transparent or translucent. Most fire opal has no play-of-colour like that of precious opal; the colour you see is the stone’s own body colour. Some stones occasionally flash bright green. Being opal, it is softer than quartz (5.5–6.5) and feels light in the hand; it should be protected from rubbing against hard surfaces. Glass and plastic (resin) imitations: man-made materials that copy the warm colours of opal; glass imitations may show round air bubbles.

On the “street to diamond” value ladder it sits on step 6 of nine: Fine ornamental and collector stone. Colour matters most for fire opal: a saturated, vivid orange or red stone that is clean and transparent is the most sought after, while pale and cloudy stones are worth less. The bright green flashes seen in some stones (play-of-colour) make a stone more special. Crack-free and large pieces, good cutting and polishing, and origin also count, and opal’s water content makes it prone to cracking, which affects value. Glass and plastic imitations and synthetic opal should not be sold as natural stone.

Today crystal-therapy sources claim that fire opal revives zest for life and creativity and gives courage and self-confidence. The same sources say the stone activates the root and sacral chakras. In Türkiye, some news websites write that opal varieties, fire opal among them, are believed to be good for eyesight and joint pain and helpful to people with kidney disorders. The warm colour of fire opal is linked to trace substances such as iron in its structure; according to a study of opal from Gümüldür, the colour is related to rising iron content. There is no scientific evidence that the stone boosts creativity, courage or energy, activates a chakra, or helps eye, joint or kidney complaints; anyone with such a complaint should see a doctor. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.