Hackmanite: the stone that changes colour in the sun

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Hackmanite is a variety of sodalite that turns pink or takes on colour in the sun, then fades in the dark. Discover tenebrescence, deposits, care and choosing.

Key points

Colour	cream white, greenish grey or pale lilac at rest; pink to violet after exposure to light
Mineral family	variety of sodalite, Na8(Al6Si6O24)(Cl,S)2, rich in sulphur
Crystal system	cubic
Hardness (Mohs)	5.5 to 6
Density	about 2.27 to 2.33
Remarkable property	tenebrescence: reversible colour change under light
Known deposits	Afghanistan (Badakhshan), Myanmar (Mogok), Greenland (Ilímaussaq), Quebec (Mont Saint-Hilaire)
Origin of the name	Victor Hackman (1866-1941), Finnish geologist

What is hackmanite?

Hackmanite is a variety of sodalite, the blue mineral of the feldspathoid group, with the formula Na8(Al6Si6O24)Cl2. It also contains a small amount of sulphur within its structure. Its name honours Victor Axel Hackman (1866-1941), a geologist with the Geological Survey of Finland. For ordinary blue sodalite, see the page on sodalite.

What makes it famous is tenebrescence: a reversible colour change under the action of light. A cream white or greenish grey piece takes on a pink, lilac or violet tint after a few moments in the sun (or under an ultraviolet lamp). Stored in darkness, it gradually regains its original colour. The effect can be repeated for a very long time, which is not the case for all stones that "change colour".

How does tenebrescence work?

The structure of sodalite forms small cages. In hackmanite, some of these cages contain sulphur atoms. Under the effect of light (especially ultraviolet), according to the literature, electrons are displaced and become trapped in tiny vacancies; together they form a colour centre that absorbs light and gives the pink-violet tint. In darkness, or under bright visible light, the electrons return to their place and the colour disappears. It is a physical phenomenon, not a treatment.

The starting colour depends on the deposit: stones from Greenland and Quebec (Mont Saint-Hilaire) are often violet when mined and then fade in the light, while those from Afghanistan and Myanmar (Mogok) are cream white and turn pink in the sun. A GIA study (2009) confirmed sulphur in all the stones examined from these last two countries, with tenebrescence strong enough to name them hackmanite. The Afghan stones also show stronger fluorescence and phosphorescence than the Burmese ones.

Traditional symbolism

A stone that wakes in the sun and falls asleep in the shade naturally appeals to lovers of symbols: it is associated with change, adaptability, the alternation of day and night, and the idea of revealing a hidden facet.

These are modern associations: hackmanite is a recent stone on the crystal market. They have no scientific basis. The phenomenon of tenebrescence, on the other hand, is real and very well documented by physics.

Traditional correspondences

Area	Correspondence cited
Chakra	third eye or crown, sometimes the heart (for the pink)
Element	air or water
Signs	Gemini, Aquarius, Pisces (very variable)
Keywords	change, adaptability, revelation

See the third eye chakra for the most frequently cited association.

How to use it

As an experiment: place the stone at a window or under an ultraviolet lamp, then hide it in an opaque box. The effect is slow: from a few seconds to a few hours depending on the piece.
As a collector's piece: a rough piece, a tumbled stone or a cabochon (guide to stone jewellery).
As a pendant or ring: the stone is hard enough for careful use; its brilliance changes with the light of the day.
For meditation: watching the colour change is an exercise in attention (tutorial).

Safety: never look directly at an ultraviolet lamp, which damages the eyes, and protect your skin. Pocket UV lamps are easy to find, but be careful around children.

Care and cleansing

Cleaning: lukewarm water, mild soap, soft cloth; dry well.
Sun: harmless for the stone; it is actually what reveals its effect. Simply keep it away from strong heat.
Heat: intense heat can erase the colour and weaken the stone (it has imperfect cleavage); avoid radiators and cars in the sun.
Knocks: hardness of only 5.5 to 6: it is scratched by quartz. Store it separately.
Acids and household products: avoid.
Salt: avoid as a precaution.

For symbolic cleansing, prefer smoke and sound (guide).

Recognising a genuine hackmanite

Sign	Natural hackmanite	To question
Colour change	pink or violet appears in the sun and disappears in shade, reversibly	fixed colour, or change that does not return
Fluorescence	orange or pink reaction under UV in many pieces	no reaction or a strange colour
Appearance	cream, grey, translucent fragments, with veins	very uniform, fixed pink or violet stone
Provenance	Afghanistan, Myanmar, Greenland, Quebec	no origin stated

The sun test is simple and safe, but it does not prove the nature of the stone on its own: some other materials also change colour under UV. For a valuable piece, ask for a gemmological laboratory certificate. See also real or fake stone and our commitments. We have not found a source documenting common imitations of hackmanite.

How to choose

Choose according to the effect: ask the seller whether the stone has been tested in light. Fine translucent pieces with an intense pink-violet after exposure are considerably more expensive than opaque fragments. To discover the phenomenon, a small rough or tumbled piece is enough.

Pairings: with blue sodalite (same mineral), lapis lazuli or amethyst. This stone is an object of curiosity and beauty, with no proven effect on health.