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, 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
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Find idocrase on the map
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