Idocrase, commonly known as vesuvianite, forms in contact-metamorphosed limestones and skarns. It is highly valued by collectors for its well-formed tetragonal prisms, which can range from earthy green to vivid yellow and even rare blue varieties like 'cyprine'.
Is this idocrase?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch idocrase with a known reference. Idocrase sits at Mohs 6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Idocrase leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Idocrase typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: green, brown, yellow, blue, red.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic crystals, massive, granular.
Often confused with
Idocrase vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside idocrase
Minerals reported to co-occur with idocrase. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₁₀Mg₂Al₄(SiO₄)₅(Si₂O₇)₂(OH)₄
- Mohs hardness
- 6.5
- Density
- 3.3-3.5 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic Crystals, Massive, Granular
- Cleavage
- Poor On {110}
- Rarity
- Common
- Uses
- Gemstone, Collector, Lapidary
- Host rock
- Metamorphic Rocks Like Skarns and Contact-metamorphosed Limestones
- Typical price
- $10-100 per specimen depending on crystal quality and origin
Where rockhounds find idocrase
7 mapped spotsClassic worldwide localities
- Mount Vesuvius, Italy
- Quebec, Canada
- California, USA
- Pakistan
- Kenya
Field-hunting tip
Look in metamorphic rocks like skarns and contact-metamorphosed limestones country — that is the host setting where idocrase typically forms. If you start seeing calcite, garnet, diopside in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, California, Nevada — start trip planning there.
Common questions
How do you identify idocrase?+
Where is idocrase found?+
Can I find idocrase in the United States?+
How much is idocrase worth?+
What rocks look like idocrase?+
What minerals are found with idocrase?+
What kind of rock does idocrase form in?+
What is idocrase used for?+
Find idocrase on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
