Madagascan Opal: Common Opal, Symbolism, Care

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“Madagascan opal” most often refers to common opal with no play of colour, dark or green, sold as spheres. It differs from the precious, iridescent opal of Australia.

Key points

Name	trade name: opal (often common opal) from Madagascar
Mineral family	opal, amorphous hydrated silica SiO2·nH2O
Water content	around 3 to 9%
Mohs hardness	5.5 to 6.5
Density	1.9 to 2.5
Special feature	usually “common” opal with no play of colour
Traditional chakra	crown, third eye, heart according to the authors

What is Madagascan opal?

Opal is hydrated silica (SiO2·nH2O), amorphous: it has no regular crystal lattice, which makes it a “mineraloid”. It contains water, generally 3 to 9%, has a hardness of 5.5 to 6.5 and a density of 1.9 to 2.5. Precious opal shows a play of colour, flashes that change with the angle: they come from light interfering in layers of tiny silica spheres stacked in regular order. Common opal has no such effect, because its spheres are smaller and disordered.

What shops call “Madagascan opal” is, in the great majority of cases, common opal: dark pieces (deep brown, almost black), green or yellow, sometimes with swirling patterns, cut into spheres, pebbles or cabochons. In our research, the Malagasy deposits named in the scientific literature are Faratsiho, near the capital, and an area near Bemia in the south-east; green common opals have also been described in the Anosy region. We could not confirm any notable production of precious play-of-colour opal in Madagascar.

Beware of the word “black”

In jewellery, a black opal is a precious opal with a dark body and a vivid play of colour, mostly from Australia, and it is a very expensive stone. When a shop sells a “black Madagascan opal” as a sphere, it is in principle a dark common opal, without play of colour and at a completely different price. The two share only the word. This is not deception if the listing says so, but the word is misleading: read the description.

Traditional symbolism

Opal has a long tradition: its name comes from the Sanskrit upala, “precious stone”, via the Greek opallion and the Latin opalus. In modern writings, it is linked to imagination, creativity and changing emotions. Dark common opal, by contrast, is described as more discreet and calm: a stone to gaze at without agitation.

These are symbolic associations, with no demonstrated effect. They vary from one author to another.

Traditional correspondences

Element	Association cited
Chakra	crown (crown chakra), third eye, sometimes heart
Element	water, sometimes air
Birthstone	opal appears in October birthstone lists (see October), not dark common opal in particular
Signs	Libra or Pisces appear in some authors’ lists, without consensus

How to use it

Decorative sphere: patterns of swirls or veins are best appreciated up close.
Pocket pebble, for its smoothness.
Cabochon or bead in occasional jewellery: opal is more fragile than quartz.
As a gift for someone who likes uncommon stones, stating honestly that it is common opal.

Care

Opal contains water and is therefore sensitive to heat, to extreme dryness and to thermal shock: a piece left for long periods near a radiator or in full sun can lose water and crack (this is called crazing). Wash it in lukewarm water with a little mild soap, wipe it dry, and avoid ultrasonic cleaners, chemical products and sudden temperature changes. Store it out of direct light, away from harder jewellery that could scratch it. For symbolic cleansing, gentle smoke or moonlight will do; see cleansing and recharging your stones.

Recognising the genuine stone and avoiding surprises

A real opal is slightly lighter than quartz of the same size (density 1.9 to 2.5) and softer than quartz (5.5 to 6.5).
Imitations in glass or resin exist, and you should be wary of large, cheap spheres that are perfectly uniform.
For precious opals, doublets and triplets (a thin layer of opal glued onto a backing) are common; a “black opal” may even be a white opal glued onto onyx.
Synthetic opals also exist. The words “laboratory opal” or “synthetic opal” must be stated explicitly.
Avoid confusion with opaline, which is glass.

How to choose

Ask whether it is common opal, where it comes from and whether it is natural. Choose a piece without cracks and with an even polish. The price of a common opal sphere is moderate. Pair it with opal, pink opal or blue opal. See also choosing and caring for your stones.