Chestermanite is a rare borate mineral belonging to the ludwigite group, typically found in contact metamorphic skarns. It usually appears as fine, needle-like or fibrous dark crystals that are best identified via micro-analysis. Collectors primarily source it from specific geological occurrences where boron-rich fluids have reacted with magnesium-rich host rocks.
Is this chestermanite?
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 chestermanite with a known reference. Chestermanite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Chestermanite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Chestermanite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, acicular, radiating masses.
Often confused with
Chestermanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Chestermanite is noticeably harder (Mohs 6 vs. 5); streak differs, so Chestermanite leaves brown, Ludwigite leaves black.
How to tell apart: Chestermanite is noticeably harder (Mohs 6 vs. 5); streak differs, so Chestermanite leaves brown, Vonsenite leaves black.
Often found alongside chestermanite
Minerals reported to co-occur with chestermanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₂(Mg₀.₅Al₀.₅)(BO₃)O₂
- Mohs hardness
- 6
- Density
- 3.84 g/cm³
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Acicular, Radiating Masses
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metasomatic Rocks and Skarns
- Typical price
- $20-150 for micro-mounts and small specimens
Where rockhounds find chestermanite
Classic worldwide localities
- Brooks Mountain, Alaska, USA
- Kola Peninsula, Russia
Field-hunting tip
Look in metasomatic rocks and skarns country, the host setting where chestermanite typically forms. If you start seeing calcite, diopside, forsterite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, radiating masses habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find chestermanite on the map
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