Gem library
Scolecite
The needle zeolite that writhes in flame
Scolecite forms sprays of white needles, long and silky, that line the geodes of the Indian basalts. It is a zeolite, that is, a mineral that holds water in open channels, and that water explains just about everything there is to say about it.
- Hardness (Mohs)
- 5 – 5.5
- Density
- 2.25 – 2.40
- Crystal system
- Monoclinic
- Refractive index
- 1.507 – 1.521
- Cleavage
- Perfect on {110}
Mineralogical identity
- Family
- Silicates, tectosilicates, zeolite group
- Species
- Scolecite
- Variety
- Scolecite in sprays
- Chemical formula
- CaAl₂Si₃O₁₀·3H₂O
- Crystal system
- Monoclinic
- Classification
- Collector's mineral
- Rarity
- Uncommon
- Indicative price
- €0.20 – 4/ct
Etymology
From the Greek skolex, «worm»: heated with a blowpipe, scolecite twists and curls like a worm as it expels its water. The name describes the experiment literally.
Physical & optical properties
- Hardness (Mohs)
- 5 – 5.5
- Density
- 2.25 – 2.40
- Refractive index
- 1.507 – 1.521
- Birefringence
- 0.007
- Cleavage
- Perfect on {110}
- Fracture
- Uneven
- Lustre
- Vitreous to silky
- Diaphaneity
- Transparent to translucent
- UV fluorescence
- Weak
- Pleochroism
- None
- Colours
- colourless, white, pale pink
Formation, geology & history
Zeolites, a hollow architecture
Scolecite belongs to the zeolites, a family of silicates whose structure is a scaffold pierced with channels at the nanometre scale. Through those channels move water molecules and cations that can come and go without destroying the edifice. It is that property that made the industrial fortune of synthetic zeolites: they are used as molecular sieves to separate gases, as catalysts in oil refining, and as softeners in detergents. The family's very name comes from the Greek zein, «to boil», and lithos: heated, these stones seem to boil as they release their water.
From the Deccan geodes
Scolecite forms at low temperature in the cavities of volcanic rocks, in company with apophyllite, stilbite and heulandite. The Deccan traps in India are the reference deposit: basalt flows erupted at the end of the Cretaceous, whose gas bubbles became geodes. The quarries of Poona and Nasik, worked for ballast, yield pieces in which sprays of scolecite radiate on a bed of chalcedony, sometimes topped by a green apophyllite. The finest associations of this kind have become museum pieces, and the progressive closure of some quarries has pushed their value up.
Fragile, and the truth about water
With a hardness of 5 and perfect cleavage, scolecite needles break at the slightest contact: a piece is handled by the matrix, never by the crystals. The stone holds three water molecules per formula unit, which it loses if heated or left in very dry air. The crystals then cloud and eventually crumble. Conversely, liquid water slowly dissolves the surface and dulls it. Scolecite is therefore one of the few minerals that must be neither wetted nor left to dry, which means: a cabinet, at a stable temperature, and hands off.
How to recognise it
- Needles in a sprayFine, long, white, silky needles radiating from a point or forming parallel bundles. Natrolite, very close, is straighter and less silky.
- LightnessDensity 2.3: among the lowest in the mineral kingdom for a compact stone. A spray of scolecite feels almost hollow in the hand.
- Hardness 5A steel point scratches it readily, glass resists it. A white needle that scratches glass is natrolite or another mineral.
Imitations, treatments & confusions
- Natrolite and mesolite sold as scoleciteThese are neighbouring zeolites, authentic, sometimes in the same geode. The distinction requires careful examination and has hardly any bearing on price.
- Reglued specimensBroken sprays are glued back. Look under a loupe for too clean a joint at the base of the needles and a glossy excess of glue.
- Reconstituted matrixDetached crystals remounted on a false base. Discreetly scratch underneath: basalt is hard and granular, tinted plaster is not.
Deposits & origins
India (Poona and Nasik, in the Deccan basalts: the world reference), Iceland, Brazil, United States (New Jersey, Oregon), Greenland, Scotland
Care & precautions
- Never water: it slowly dissolves the surface and loosens the needles from their matrix.
- Dust by blowing, at most with a very soft brush. The needles break under the slightest rubbing.
- Away from any heat source: the stone loses its structural water and clouds permanently.
- A closed cabinet, at a stable temperature, and handling by the matrix only.
Traditions & crystal healing
- Chakras
- Crown · third eye
- Zodiac signs
- Cancer · Pisces
- Element
- Air
It is presented as a stone of appeasement and sleep, often associated with apophyllite, alongside which it grows. Its whiteness and fineness earn it a reputation for gentleness. Cultural heritage, never medicine.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Can a scolecite be cleaned with water?
No, and this matters. Water slowly dissolves the surface and detaches the needles. A puff of air is the only sensible cleaning.
Why have my needles turned opaque?
The stone has dried or been heated, and has lost part of its structural water. The process is irreversible: keep it away from radiators and direct sun.
Scolecite or natrolite?
Very close. Scolecite is monoclinic and its needles are slightly silky and sometimes curved; natrolite is orthorhombic, stiffer and glassier. The two often live together.
Tools for this stone
Scolecite: only the tools this stone actually concerns, each carrying the value read on this page.