Diopside is a mineral with a hardness of 6 out of 10 on the Mohs scale of mineral hardness [?]. These Monoclinicly structured gems are made of calcium magnesium silicate, their full chemical compound being CaMg(SiO3)2.
Diopside is a type of Clinopyroxene, which are abundant, rock-forming minerals. These are embedded and surface-growing crystals, short columnar, and tabular, almost square or octagonal in cross section. It is the magnesium-bearing end member in the isomorphous, monoclinic diopside-hedenbergite series, a complete solid solution series in which two intermediate members, salite and ferrosalite, have been identified.
It is a silicate of calcium and magnesium.
It is bronzy, metallic-looking, with perfect cleavage. It appears more often in granular, rodlike or fibrous, radiating aggregates, in pale-green, blue, white, yellow, or brown. It is transparent to translucent with vitreous luster. Its color ranges from bottle green to blackish green, but also bright green or dull yellowish green. In some cases it is semiopaque, with internal fibrosity.
It fuses with difficulty to a green glass and is insoluble in acids.
Along with hedenbergite, it occurs in igneous and metamorphic rocks, diopside particularly in metamorphosed impure limestone, and in dolomitic marbles associated with other calcium silicates. It also appears in metasomized seams or lenses in serpentinized rocks (rodingites). Chromium-bearing diopside is typical of kimberlites. Salite is typical of some hypabyssal rocks derived from alkaline basalt magmas, and comes from Sala (Sweden), and other places in Finland, Scotland, Greenland, and New Zealand. Ferrosalite has been discovered in gneiss and metasomized contact rocks (skarns) in Fabian Mine (Sweden) and in St. Lawrence County, New York (USA).
Magnificent, clear, often complex crystals are found in Italy - in Val di Fassa (Trento), in calcareous blocks ejected by Vesuvius, as Monte Cervandone (Val d'Ossola), alalite from Pian della Mussa in Val d'Ala (Turin), in the Binnental (Switzerland), and at DeKalb and Gouverneur, New York (USA). Deposits are also found in Erzebirge (Germany), the Zillertal (Austria), baikalite, a dark green variety from the Urals and Lake Baikal (Soviet republics), Nordmarken (Sweden), cat's-eye chrome diopside from Myanmar (Burma).
Its bright, emerald-green variety is called "chrome diopside" and is a gemstone. Its dark-green form contains vanadium and is called "lavrovite," or "chrome enstatite." These come from kimberlites in South Africa and Siberia.
The purple manganese-bearing variety is known as "violane." This is typical of St. Marcel (Val d'Aosta, Italy).
Diopside displaying asterism when the stone is cut en cabochon is called "star diopside," and is seen quite often on the market for minor gemstones. Star stones with four notably sharp rays come from Myanmar, and four-rayed star diopside has been reported from southern India. It has only binary symmetry, and the star has four rays, two of which are straight, while the other two, not at right angles to the first pair, look slightly wavy. Sometimes, oriented needlelike surface crystalline inclusions are clearly visible, especially from below. It is sometimes passed off as "star sapphire," although the resemblance is highly superficial.
The variety of various colored granular diopside is called "coccolite."
Other names for diopside include "alacolite," "chromdiopside,"
Misleading terms include "chloromelanite jade" for gem quality green diopside resembling jade.
"Diopside jadeite" or "Diopside jade" is a pyroxene intermediate between jadeite and diopside from Tuxtla, Mexico.
Diopside derives its name from the Greek "dis" and "opsis" meaning "double vision," because it is clearly birefringent. Some of the magnesium may be replaced by iron.
Some transparent varieties are faceted into gems. the semiopaque specimens exhibit chatoyancy or asterism if appropriately cut. It is not a very well-known gem, outside the areas where it is mined and cut. The brilliant green chrome diopside varieties are of low value. The dark or light green varieties are worth still less. It is neither imitated nor produced synthetically. But the mineral is of interest to collectors and petrologists.