Vesuvianite

The name vesuvianite is geographic. The species was first recognised in blocks of altered limestone thrown up by Mount Vesuvius, the volcano on the Bay of Naples, and the name carries that locality forward.

The first stones reached the literature long before they had a settled name. In 1723, the Swiss naturalist Moritz Anton Kappeler described them under the unwieldy label hyacinthus dictus octodecahedricus — the eighteen-faced hyacinth, hyacinth being a yellow-to-brown gem variety of zircon the crystals resembled in colour. Half a century later, in 1772, the French crystallographer Jean-Baptiste Louis Romé de L'Isle rebaptised them hyacinte du Vésuve — Vesuvius hyacinth — naming the locality for the first time. That phrase appears to have inspired the German mineralogist Abraham Gottlob Werner. In 1795, he dropped the hyacinth comparison and named the species vesuvian after its discovery locality. Werner's name became the modern one.

A second name appeared almost immediately. In 1799, the French mineralogist René Just Haüy introduced idocrase, built from Greek roots meaning mixed form, in reference to the varied crystal habits the species showed. Idocrase was for a long time the more popular name and is still common in the gem trade, but vesuvianite is the form the International Mineralogical Association recognises.

The species has produced several named varieties that carry their own short stories. Cyprine is a sky-blue form first reported from Franklin, New Jersey, its colour traced to traces of copper. Xanthite is a manganese-rich form. The most commercially conspicuous is californite, a compact green vesuvianite from several California localities that resembles jade closely enough to be marketed as California jade or American jade — names that are gemmological convention rather than mineralogical truth, since the stone is neither jadeite nor nephrite.

Vesuvianite has no industrial role of any scale. It is not mined as an ore, not used as an abrasive, not consumed in any chemical process. Its working life today divides cleanly between the gem trade and the petrologist's hand lens.

As a gem and ornamental stone

Transparent crystals of clean green or brown colour are sometimes cut as faceted gemstones, sold under either vesuvianite or the older trade name idocrase. Volume is modest — the species is not in the major gemstone tier — and most of the demand sits with collectors of unusual cut stones rather than the broad jewellery market.

The more commercial form is californite, a compact, opaque green vesuvianite found at several California localities. Its even colour and high polish let it stand in for jade, and it is cut into cabochons — domed, unfaceted stones — and carved into beads and small ornaments, sold as California jade or American jade. The trade names are gemmological convention; californite is neither jadeite nor nephrite. Cyprine, the sky-blue copper-bearing variety from Franklin, New Jersey, and xanthite, the yellow manganese-rich variety, occasionally appear in collector-grade cut stones but carry no commercial gem market.

As a research mineral

Outside the gem trade, vesuvianite's most consistent use is as an index mineral for the petrologist — the geologist who reads rock origins from mineral assemblages. The species forms when calcium-rich rocks are cooked and chemically altered by an intruding hot body, and finding it in an outcrop is itself a clue to that history. It is a characteristic mineral of skarns — the calcium-silicate rocks produced when a granite intrusion bakes a neighbouring limestone. It also appears in limestones that have undergone contact metamorphism more broadly. Museums and university collections maintain a steady, modest demand for well-crystallised specimens from classic localities — Mount Vesuvius, the Ala Valley in Piedmont, and the Wiluy River in Siberia chief among them.