Diopside is a calcium magnesium silicate in the pyroxene group of minerals. Its best-known gem form is chrome diopside, a vivid green stone from Siberia that is often compared to emerald and tsavorite. India produces black star diopside, which shows a four-rayed star. Diopside is softer than most jewelry gems and has two cleavage directions, so it suits earrings and pendants better than everyday rings.
What diopside is
Diopside forms in metamorphic rocks such as marble and skarn, and in some igneous rocks rich in magnesium. It is common as a rock-forming mineral, but clean, well-colored crystals large enough to cut are much rarer. Iron gives ordinary diopside a bottle-green to brown color. Chromium gives the bright green of chrome diopside.
The name comes from Greek words meaning "two" and "view" or "appearance," a reference to the two ways its prism can be oriented. The pyroxene group also includes jadeite, one of the two minerals sold as jade.
Diopside is a doubly refractive mineral with fairly high birefringence. In larger faceted stones you may see facet edges doubled when looking through the stone, an effect described on the page about birefringence and double refraction.
Chrome diopside
Siberian deposits
Chrome diopside comes mainly from eastern Siberia in Russia. Deposits there were known in the Soviet era, but the material reached the international gem market in quantity only after the Soviet Union broke up in the early 1990s. Russian chrome diopside is sometimes sold as "Siberian emerald," a misleading name that should not be used.
Chrome diopside also comes from Pakistan, Finland, South Africa and elsewhere, usually in smaller amounts. Small green chrome diopside grains are also a familiar "indicator mineral" in the search for diamonds, because they are carried to the surface in kimberlite. The page on diamond geology explains how prospectors use these grains.
Color and size
Fine chrome diopside is an intense, slightly yellowish to pure green with good saturation. The color comes from chromium, the same element responsible for the green of emerald. The difference is that chrome diopside's color deepens quickly with size. Stones above about two carats often look too dark, almost blackish green. For that reason most chrome diopside is cut in small sizes, and stones of one or two carats tend to show the best color.
Chrome diopside is usually clean to the eye. It is rarely treated, which adds to its appeal for buyers who prefer untreated gems.
An emerald alternative
Chrome diopside is often recommended as an affordable alternative to emerald or tsavorite garnet. It offers a similar vivid green at a far lower price, with better clarity than most emeralds. The trade-off is durability. Emerald is 7.5 to 8 on the Mohs scale, and tsavorite about 7 to 7.5, while diopside is only 5.5 to 6.
Star diopside and other varieties
Black star diopside
Black star diopside comes mainly from southern India. It is opaque, very dark green to black, and cut as cabochons to show a four-rayed star. The star comes from fine needle-like inclusions, often magnetite, aligned in two directions. Because the rays usually do not cross at right angles, the star often looks like a stretched X instead of a perfect cross.
The magnetite inclusions make star diopside weakly magnetic, which helps separate it from black star sapphire. A strong magnet will often pull on a loose stone. Black star diopside can also show chatoyancy instead of a full star, sold as cat's eye diopside.
Other colors
Diopside also occurs in yellow, brown, colorless and violet. Violet diopside, called violane, comes from Italy and is usually opaque. These are mostly collector stones.
Softness and cleavage
Diopside's main drawback for jewelry is durability:
- At Mohs 5.5 to 6, it is softer than quartz, which makes up much of household dust. Over time, dust and contact will dull and scratch it.
- It has two good cleavage directions at roughly 90 degrees. A sharp knock along those planes can split the stone.
- It is moderately brittle, so facet edges chip if they hit hard surfaces.
Cutters orient stones to keep cleavage planes away from the table and girdle where possible. The page on cleavage in gemstones explains why this matters for both cutting and setting.
Wearing and caring for diopside
Earrings, pendants and brooches are the safest settings. If you choose a diopside ring, use a protective setting such as a bezel or low-profile mounting, and take it off for physical work, sports and cleaning. The gemstone settings page compares how different settings guard a stone.
Clean diopside with lukewarm soapy water and a soft brush. Avoid ultrasonic and steam cleaners, since vibration and heat can open cleavage planes. Store it separately so harder gems do not scratch it. For a gem-by-gem guide, see how to clean jewelry safely.
Identifying diopside
Chrome diopside can look like emerald, tsavorite, peridot or green tourmaline. A refractometer reading of about 1.67 to 1.70, with fairly high birefringence, sets it apart. Peridot has a similar refractive index but a different birefringence and spectrum. Chrome diopside also shows chromium lines in a spectroscope and often turns reddish under a Chelsea filter.
Frequently asked questions
Is chrome diopside a good emerald substitute?
It gives a similar vivid green at a lower price and is usually cleaner than emerald. It is much softer, so it is better for earrings and pendants than for daily-wear rings.
Why are large chrome diopsides rare?
Large stones exist, but chrome diopside darkens quickly with size. Stones above about two carats often look too dark, so most fine stones are small.
Is black star diopside magnetic?
Often, yes. Magnetite inclusions that create the star also make the stone weakly magnetic, which helps separate it from black star sapphire.
Is diopside treated?
Diopside is rarely treated. Most chrome diopside on the market has natural, untreated color.