Gem library
Vesuvianite
Idocrase, born on the flanks of Vesuvius
Vesuvianite was born in the limestone blocks thrown out by Vesuvius, where magma had baked the rock. Under the name californite, its massive green variety was long sold as jade, and the confusion is not quite extinct.
- Hardness (Mohs)
- 6 – 7
- Density
- 3.32 – 3.47
- Crystal system
- Tetragonal
- Refractive index
- 1.700 – 1.723
- Cleavage
- Poor on {110}
Mineralogical identity
- Family
- Silicates, sorosilicates
- Species
- Vesuvianite
- Variety
- Idocrase, californite
- Chemical formula
- Ca₁₀(Mg,Fe)₂Al₄(SiO₄)₅(Si₂O₇)₂(OH)₄
- Crystal system
- Tetragonal
- Classification
- Semi-precious stone
- Rarity
- Uncommon
- Indicative price
- €2 – 80/ct (blue cyprine: far beyond)
Etymology
Named in 1795 by Werner after Vesuvius, where it was discovered in the blocks thrown out by the volcano. Its synonym, idocrase, comes from the Greek eidos, «form», and krasis, «mixture», because its crystals seem to borrow the forms of other minerals.
Physical & optical properties
- Hardness (Mohs)
- 6 – 7
- Density
- 3.32 – 3.47
- Refractive index
- 1.700 – 1.723
- Birefringence
- 0.001 – 0.012
- Cleavage
- Poor on {110}
- Fracture
- Uneven to conchoidal
- Lustre
- Vitreous to resinous
- Diaphaneity
- Transparent to opaque
- UV fluorescence
- None
- Pleochroism
- Weak
- Colours
- green, olive green, brown, yellow, blue
Formation, geology & history
A contact mineral
Vesuvianite forms at the contact between a magma and a limestone: heat and fluids transform the carbonate rock into a new rock, skarn, in which grossular garnet, diopside, wollastonite and vesuvianite crystallise. The blocks ejected by Vesuvius during the eighteenth-century eruptions contained magnificent crystals of it, and that is where it takes its name. The deposits of Val d'Ala, in Piedmont, and those of the Urals give the finest crystals. In Quebec, the asbestos mines of Asbestos yielded for decades green and pink pieces of world quality, now sought after by collectors.
Californite, cyprine and the others
Vesuvianite comes in several commercial varieties. Californite is its massive form, apple green to olive green, compact, closely resembling nephrite jade: it was sold as «California jade» throughout the early twentieth century, and is still sometimes presented that way. Cyprine, charged with copper, is blue to blue-green, rare and expensive; it comes mainly from Norway. There are also transparent brown crystals from Burma and Pakistan, facetable, and a yellow material from Kenya. The pink manganoan variety, from the Jeffrey Mine in Quebec, is among the most prized by collectors.
An honest stone to wear
Hardness 6 to 7, no really troublesome cleavage, good toughness in the massive variety: vesuvianite wears well. Californite is cut into cabochons and objects like jade, and stands daily wear. Faceted transparent crystals are more delicate but still robust. The only real pitfall is commercial: the stone is little known, often misidentified, and a seller who does not know what he is selling labels it now jade, now epidote, now peridot. The price suffers, in both directions.
How to recognise it
- The tetragonal prismThe crystals are square-based prisms, often stubby, capped by a low pyramid. Very different from garnet, which crystallises in twelve-faced balls.
- Resinous lustreOn a fracture, vesuvianite has a slightly greasy lustre, between glass and resin, characteristic and fairly recognisable to the naked eye.
- Density3.4: distinctly heavier than nephrite jade (3.0) and than serpentine (2.6), at equal volume. It is the best test for settling a californite.
Imitations, treatments & confusions
- Californite sold as jadeThe classic. It is not glass, it is a real stone, but it is not jade and the price should not be jade's. Density and toughness settle it.
- Confusion with epidote and peridotEpidote is pistachio green and crystallises in striated blades; peridot is yellower and far more birefringent. Honest errors, frequent among resellers.
- Green glassOn beads. Bubbles, warmth to the touch, and a density of 2.5 instead of 3.4.
Deposits & origins
Italy (Vesuvius, Val d'Ala), Canada (Quebec, Asbestos), United States (California, hence californite), Russia (Urals), Pakistan, Kenya, Norway
Care & precautions
- Warm soapy water and a soft brush: the stone is robust and does not mind water.
- Ultrasonics acceptable on a sound piece, to be avoided on a fissured crystal.
- Fears neither light nor ordinary heat.
- Store separately, it scratches softer stones and is scratched by quartz.
Traditions & crystal healing
- Chakras
- Heart · solar plexus
- Zodiac signs
- Capricorn · Sagittarius
- Element
- Earth
It is described as a stone of quiet courage and of release from old loyalties, often proposed as a substitute for jade by those looking for a more affordable green stone. 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
Vesuvianite or idocrase?
Both names mean the same mineral. «Vesuvianite» is the official name, «idocrase» an old synonym still much used in the trade.
Is californite jade?
No. It is massive vesuvianite, and it has the look but neither the composition nor the toughness. Density, 3.4 against 3.0, settles it.
Why is it so little known?
Because it has no strong trade name and it resembles other, better-established stones. That is precisely what makes it a good buy for a collector.
Tools for this stone
Vesuvianite: only the tools this stone actually concerns, each carrying the value read on this page.