Gem library
Chrome diopside
Siberian green, cut like emerald
Chrome diopside is the most intense green stone you can buy at a reasonable price. It owes its colour to the same chromium as emerald, comes from a single deposit in Siberia, and has only one failing: you almost never find it above two carats.
- Hardness (Mohs)
- 5.5 – 6.5
- Density
- 3.22 – 3.38
- Crystal system
- Monoclinic
- Refractive index
- 1.664 – 1.730
- Cleavage
- Distinct on {110}
Mineralogical identity
- Family
- Silicates, inosilicates, pyroxene group
- Species
- Diopside
- Variety
- Chromian diopside
- Chemical formula
- CaMgSi₂O₆ + Cr
- Crystal system
- Monoclinic
- Classification
- Semi-precious stone
- Rarity
- Uncommon
- Indicative price
- €10 – 120/ct (above 2 ct: far more)
Etymology
From the Greek dis, «twice», and opsis, «sight»: the prism can be oriented two ways, giving two images of the same crystal.
Physical & optical properties
- Hardness (Mohs)
- 5.5 – 6.5
- Density
- 3.22 – 3.38
- Refractive index
- 1.664 – 1.730
- Birefringence
- 0.024 – 0.031
- Cleavage
- Distinct on {110}, two directions at 87°
- Fracture
- Uneven
- Lustre
- Vitreous
- Diaphaneity
- Transparent
- UV fluorescence
- None
- Pleochroism
- Distinct
- Colours
- green, deep green, bottle green
Formation, geology & history
One deposit, and why
Diopside is a commonplace mineral, present in metamorphosed limestones and ultrabasic rocks the world over. But transparent, intensely green, facetable diopside is quite another matter: it comes essentially from the Inagli massif, in the Republic of Sakha, in the heart of eastern Siberia. The crystals grow there in veins associated with ultrabasic rocks, in company with chromite, which supplies the colouring chromium. The site is accessible only part of the year, by frozen tracks, which explains the jolts in supply. The stone was first sold as «Siberian diopside», then, around the 1990s, as chrome diopside, which says better where the colour comes from.
Chromium, the same as emerald
The green comes from trivalent chromium substituting for part of the magnesium, exactly as in emerald and tsavorite garnet. The tint is frank, deep, a little darker than emerald's, and it has one peculiarity: above about two carats the stone becomes so dark that it looks almost black in weak light. That is a structural constraint, not a defect of quality, and it is why fine stones stay small. Lapidaries compensate by cutting shallow pavilions that let more light through.
A delicate stone to wear
With a hardness of 5.5 to 6.5 and distinct cleavage in two directions at 87 degrees, diopside demands consideration. It should not be set in a ring worn every day: a facet edge chips at the first contact with a worktop. As a pendant and as earrings it holds up very well. Pleochroism is marked, from yellowish green to bluish green depending on direction, and a good lapidary orients the table to catch the richest tint. There is also a star diopside, black and four-rayed, and a cat's eye diopside, both Siberian.
How to recognise it
- Distinct pleochroismTurn the stone in front of a lamp: the green should shift from yellowish to bluish. Emerald, by contrast, shows far more discreet pleochroism.
- Cleavage at 87 degreesOn the girdle or the pavilion, under a loupe, two families of cleavage planes meet at very nearly a right angle. That is the pyroxene signature.
- Moderate hardnessA steel file bites it, which happens to neither emerald (7.5) nor tsavorite garnet (7). To be tested on the pavilion, never on the table.
Imitations, treatments & confusions
- Green glassLighter, with no pleochroism, with bubbles and rounded facet edges. The simplest test remains hardness.
- Tsavorite garnet announced as diopside, or the reverseTsavorite is harder, dearer, and has neither cleavage nor pleochroism. The confusion always runs in the same direction, the seller's.
- Colour-treated diopsideNot common, but pale stones are sometimes irradiated. A uniform tint with no zoning, on a large very light stone, deserves a question.
Deposits & origins
Russia (Inagli, in Yakutia: almost all the gem material), Pakistan, Burma, Italy (Val d'Ala), Canada, South Africa, Finland
Care & precautions
- Warm soapy water and a soft cloth. A brief rinse, dried at once.
- Never ultrasonics or steam: cleavage in two directions gives way under vibration.
- Avoid wearing it as an everyday ring, prefer a pendant and earrings.
- Store separately, the stone is scratched by quartz and anything harder.
Traditions & crystal healing
- Chakras
- Heart
- Zodiac signs
- Taurus · Virgo
- Element
- Earth
Associated with the heart and with appeasement, it is presented as a stone of repair after an ordeal. Its reputation is recent, the material having reached the Western market only after the fall of the Soviet Union. 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
Why are there no large stones?
Above about two carats, chromium saturation makes the stone nearly black. Large stones exist but lose all brilliance, so the market does not want them.
Can it be worn as a ring?
As a dress ring, yes; as an everyday ring, no. Hardness 6 and cleavage in two directions: the edges chip on contact.
Chrome diopside or emerald?
Emerald is harder, lighter in tone, often included and ten to a hundred times dearer. Diopside is darker, cleaner and very affordable. They are not competitors.
Tools for this stone
Chrome diopside: only the tools this stone actually concerns, each carrying the value read on this page.