Vesuvianite is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Tetragonally structured gems are made of calcium aluminum silicate, their full chemical compound being Ca6Al(Al,OH)(SiO4)5.
Vesuvianite is a hydrous calcium magnesium aluminum silicate with a tetragonal crystal system. It is the preferred name used by mineralogists for all transparent varieties of Idocrase, the name used by gemmologists.
It is a gem mineral that appears in diverse colors, and thus is prized by collectors. A compact green variety of vesuvianite that looks like jade is known as californite. A greenish-blue or sky-blue variety is named cyprine because it contains copper. A transparent yellowish-brown type is known as xanthite.
It appears in stubby, prismatic crystals, in rare cases as dipyramidal, like two pyramids connected at their bases. Usually it appears in aggregates, sometimes columnar, with fine parallel lines. It also appears in compact granular masses, in colors of brown, olive green, or more rarely, yellow, red, and blue.
It is hard, heavy, fragile, with shell-like fracture. It is usually opaque, but its translucent and transparent varieties have vitreous to resinous luster. It fuses fairly easily into greenish or brown blistered glass, and is virtually insoluble in acids.
Vesuvianite is a mineral typical of contact metamorphic skarns that contain calcium carbonate. It is associated with various kinds of garnets (grossular, andradite), wollastonite, epidote, phlogopite, and diopside. Its high calcium content reflects its occurrences in limestones.
Brown or yellow crystals have been found in the high-calcium carbonate blocks ejected by Vesuvius and Monte Somma (Italy), where the mineral was first identified. Perfect crystals were found in the contact aureole of Monzoni (Val di Fassa, Trento).
Green or yellowish-green vesuvianite has been found in lithoclases of Alpine rodingites in Val d'Ala (Piedmont), Valle della Gava (Liguria), Val Malenco (Sondrio), all in Italy, and at Zermatt (Switzerland). Also at Litchfield (Canada), Fresno, California (USA), and in various localities in the Urals. The pale-blue variety (cyprine) comes from Arendal (Norway), pale green or whitish (wiluite) from Siberia (Russia) and yellow (xanthite) from Amity, New York (USA).
A massive, microgranular variety, white speckled with green (californite) is found in Siskiyou, Fresno, and Tulare counties, California, and in Oregon (USA).
Fine vesuvianite also comes from Mexico (Morelos and Chiapas) and in Italy is found in tuffs in Lazio, from Sardinia, and more rarely from contact metamorphic rocks in Adamello (Val Camonica) and Val d'Aosta.
Varieties of vesuvianite include:
Californite - a massive, translucent to opaque, green-yellow to dark green variety that looks a lot like jade, and indeed it is used as a substitute for poor-quality jade. This usually comes from Fresno, Siskiyo, and Tulare counties in California and in Pakistan. It is erroneously named Oregon jade, American jade, and California jade. In its compact form, californite vesuvianite can be difficult to tell visually from true jade. Fushanshi is a Chinese term for vesuvianite used as jade.
Chrome idocrase - an emerald-green, chromium-bearing variety of vesuvianite which is used as a gemstone.
Colophonite - a name for a non-gem variety of vesuvianite from Arendal, Norway.
Cyprine - synonym for a variety of vesuvianite or idocrase found in Telemark (Norway), containing a trace of copper with pale-blue to sky-blue or greenish-blue color.
Egeran - a brown or yellowish-green variety of vesuvianite from Eger in western Hungary, and Germany.
Massive forms of vesuvianite are often mistaken for diopside, epidote, or garnet.
Vesuvianite is also called vesuvian, chrome-vesuvian, genevite, wiluite, duparcite, laurelite, and pyramidal garnet.
This mineral is called "vesuvianite" after a green variety found in blocks of dolomitic limestones erupted from Mount Vesuvius in Italy. The name "idocrase" is from the Greek "eidos" meaning "likeness," and "krasis" meaning "mixture," describing its similarity to other minerals.
The californite variety of vesuvianite, and other transparent varieties are used for jewelry. It is also of interest to petrologists and collectors.
Gem crystals of vesuvianite are rare. Fine, greenish-yellow, transparent gems are those which have been cut from fine crystal coming from Laurel, Quebec, Canada, or greenish-golden color with small veil-type inclusion from European sources. The massive stones are cut cabochon. Most vesuvianite used in jewelry is in smoothly polished, rounded shapes.