Ilvaite is a striking, iron-rich silicate typically found in black, vertically striated prismatic crystals. It is most frequently encountered in contact metamorphic zones known as skarns, where it forms in association with other calc-silicate minerals. Collectors often prize it for the sharp, well-defined crystal habits that can sometimes form large, impressive clusters.
Is this ilvaite?
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 ilvaite with a known reference. Ilvaite sits at Mohs 5.5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black, inclining to green or brown.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: iron black, dark grayish black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: columnar, massive, striated.
Often confused with
Ilvaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Tourmaline is the harder of the two (Mohs 7-7.5 vs. 5.5-6); streak differs, so Ilvaite leaves black, inclining to green or brown, Tourmaline leaves white; luster reads submetallic on Ilvaite and vitreous on Tourmaline.
How to tell apart: Streak differs, so Ilvaite leaves black, inclining to green or brown, Arfvedsonite leaves deep bluish gray, gray-green; luster reads submetallic on Ilvaite and vitreous on Arfvedsonite.
Often found alongside ilvaite
Minerals reported to co-occur with ilvaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe²⁺₂Fe³⁺(Si₂O₇)O(OH)
- Mohs hardness
- 5.5-6
- Density
- 3.99-4.05 g/cm³
- Colors
- Iron blackDark grayish black
- Streak
- Black, inclining to green or brown
- Luster
- Submetallic
- Transparency
- Opaque, translucent in fine fragments
- Crystal system
- Orthorhombic
- Crystal habit
- Columnar, massive, striated
- Cleavage
- Distinct on {001} and {010}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In contact metasomatic rocks and iron deposits; in metamorphosed limestones and dolostones with other calc-silicate minerals
Where rockhounds find ilvaite
Classic worldwide localities
- Laxey mine, South Mountain, Owyhee Co., Idaho, USA
- Middlemarch Pass, Dragoon Mountains, Cochise Co., Arizona, USA
- Copper Mountain, Prince of Wales Island, Alaska, USA
- Elba, at Rio Marina and Capo Calamita, Italy
- Mt. Mulatto, near Predazzo, Trentino-Alto Adige, Italy
- Seriphos, Cyclades Islands, Greece
Field-hunting tip
Where it forms: In contact metasomatic rocks and iron deposits; in metamorphosed limestones and dolostones with other calc-silicate minerals. If you start seeing quartz, magnetite, hedenbergite in float, you are in the right ground. Typical habit: columnar, massive, striated. Train your eye for that shape before scanning the outcrop.
Common questions
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Find ilvaite on the map
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