Warwickite is a rare borate mineral that typically forms elongated or prismatic dark-colored crystals in metamorphosed limestones. It is most famous for its occurrence in the contact metamorphic zones of the New York Highlands, where it appears alongside various magnesium-rich silicates.
Is this warwickite?
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 warwickite with a known reference. Warwickite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: bluish black.
- 3Read the lusterHold the specimen under a strong light. Luster: subvitreous to pearly, submetallic on cleavages, commonly dull if altered.
- 4Match the color rangeCompare against the expected color range: black, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crystalline, prismatic.
Often confused with
Warwickite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Ludwigite is the harder of the two (Mohs 5-5.5 vs. 3.5-4); streak differs, so Warwickite leaves bluish black, Ludwigite leaves black to greenish black; luster reads subvitreous to pearly, submetallic on cleavages, commonly dull if altered on Warwickite and submetallic on Ludwigite.
How to tell apart: Streak differs, so Warwickite leaves bluish black, Szaibélyite leaves white; luster reads subvitreous to pearly, submetallic on cleavages, commonly dull if altered on Warwickite and silky to dull on Szaibélyite.
Often found alongside warwickite
Minerals reported to co-occur with warwickite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mg,Ti,Fe,Cr,Al)₂O(BO₃)
- Mohs hardness
- 3.5-4
- Density
- 3.34-3.36 g/cm³
- Streak
- Bluish black
- Luster
- Subvitreous to pearly, submetallic on cleavages, commonly dull if altered
- Transparency
- Opaque, transparent in thinnest edges
- Crystal system
- Orthorhombic
- Crystal habit
- Crystalline, prismatic
- Cleavage
- On {100}, good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare accessory mineral in boron-metasomatized limestone and associated skarns; in lamproitic rocks and carbonatitelike veinlets cutting them
Where rockhounds find warwickite
Classic worldwide localities
- Found near Bancroft, Ontario, Canada
- La Ceila, near Jumilla, Murcia Province, Spain
- Tayozhnoye iron deposit, 550 km south of Yakutsk, and the Taiga borate-magnetite deposit, Sakha, Siberia, Russia
- Hol Kol Au–Cu mine, about 75 km southeast of Pyongyang, Suan Co., North Korea
Field-hunting tip
Where it forms: A rare accessory mineral in boron-metasomatized limestone and associated skarns; in lamproitic rocks and carbonatitelike veinlets cutting them. If you start seeing chondrodite, szaibélyite, sinhalite in float, you are in the right ground. Typical habit: crystalline, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find warwickite on the map
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