How to Identify Vesuvianite (Idocrase): The Volcanic Mineral Collectors Love

July 16, 2026

What Is Vesuvianite?

Vesuvianite — also known by its older name idocrase — is a calcium aluminum silicate mineral first described from specimens found on the slopes of Mount Vesuvius in Italy, giving it one of the most dramatic origin stories in mineralogy. Today it is prized by collectors worldwide for its rich green, yellow, and brown colors, glassy luster, and well-formed tetragonal crystals.

Despite being less famous than tourmaline or garnet, vesuvianite rivals both in beauty and variety, and fine specimens from top localities command serious attention at mineral shows and auctions.

Key Identification Features

Learning to identify vesuvianite in the field or at a show comes down to a handful of reliable characteristics:

Crystal system: Tetragonal — vesuvianite forms short prismatic to pyramidal crystals with a distinctive square cross-section.
Color: Most commonly olive green to yellow-green, but also brown, yellow, purple (rare), and colorless. The vivid green variety from California is sometimes called californite and is occasionally mistaken for jade.
Luster: Vitreous (glassy) to resinous on crystal faces; waxy on massive material.
Hardness: 6–7 on the Mohs scale — it will scratch glass easily and resist a steel knife blade.
Streak: White to colorless.
Cleavage: Poor in two directions; vesuvianite tends to fracture rather than cleave cleanly.
Specific gravity: 3.3–3.5 — noticeably heavy for its size compared to quartz or calcite.
Transparency: Transparent to translucent in crystals; opaque in massive form.

Vesuvianite vs. Similar Minerals

vs. Epidote: Epidote has a monoclinic crystal system with striated prismatic crystals and a pistachio-green hue. Vesuvianite crystals are stubbier with a square cross-section.
vs. Grossular Garnet: Grossular is isometric (dodecahedra/trapezohedra); vesuvianite is tetragonal. The two often occur together in skarns.
vs. Jade: Massive californite vesuvianite is sometimes sold as American jade. True jade is tougher; a specific gravity test confirms the difference.
vs. Tourmaline: Tourmaline has a triangular cross-section and strong lengthwise striations. Vesuvianite crystals are square in cross-section and lack those striations.

Famous Localities

Mount Vesuvius, Italy — The type locality; classic brown and yellow crystals in calcite skarns.
Asbestos & Jeffery Mine, Quebec, Canada — Exceptional green crystals among the finest in the world.Also the manganoan variety (purple) can be found here.
Val d'Ala, Piedmont, Italy — Superb yellow-green crystals on matrix.
Fresno County, California, USA — Source of massive green californite.
Outokumpu, Finland — Rare purple vesuvianite (wiluite).
Pakistan and Afghanistan — Gem-quality transparent green and yellow material.

Formation

Vesuvianite is primarily a contact metamorphic mineral, forming in skarns where hot magmatic fluids react with calcium-rich limestone or dolomite. It also occurs in serpentinites, rodingites, and regionally metamorphosed marbles. Its typical associates — grossular garnet, diopside, wollastonite, and epidote — are reliable field clues to its presence.

Caring for Your Vesuvianite Specimens

Cleaning: Warm water and a soft brush. Avoid ultrasonic cleaners.
Acids: Dilute acids can etch vesuvianite surfaces — test on an inconspicuous area first.
Storage: Keep away from harder minerals like quartz or topaz. Use padded trays or individual boxes.
Handling: Hold by the matrix, not by crystal clusters, to protect terminations.

Vesuvianite as a Gemstone

Transparent vesuvianite is occasionally faceted into gems (sometimes sold as idocrase in the gem trade). Californite cabochons are popular in lapidary work as an affordable jade alternative. Fine faceted vesuvianite is a genuine collector's gem — rare in cut form with attractive color and good hardness.