Magnesiohulsite is a rare tin-bearing borate mineral typically found in skarns formed by the interaction of granite intrusions with limestone. It appears as dark, prismatic to granular masses that are difficult to distinguish from other borate minerals like ludwigite without chemical analysis. Collectors often seek it as a rare species representative for suite building in tin-borate localities.
Is this magnesiohulsite?
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 magnesiohulsite with a known reference. Magnesiohulsite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Magnesiohulsite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Magnesiohulsite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, massive.
Often confused with
Magnesiohulsite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Magnesiohulsite leaves black, Hulsite leaves brownish-black.
How to tell apart: Ludwigite is the harder of the two (Mohs 5 vs. 3-4).
How to tell apart: Vonsenite is the harder of the two (Mohs 5 vs. 3-4).
Often found alongside magnesiohulsite
Minerals reported to co-occur with magnesiohulsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mg,Fe²⁺)₂SnBO₅
- Mohs hardness
- 3-4
- Density
- 4.15 g/cm³
- Colors
- Streak
- Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metasomatized Carbonate Rocks in Contact Metamorphic Zones
- Typical price
- $50-300 per specimen
Where rockhounds find magnesiohulsite
Classic worldwide localities
- Brooks Mountain, Alaska, USA
- Sichuan Province, China
- Yakutia, Russia
Field-hunting tip
Look in metasomatized carbonate rocks in contact metamorphic zones country — that is the host setting where magnesiohulsite typically forms. If you start seeing calcite, magnetite, fluorite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesiohulsite?+
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How much is magnesiohulsite worth?+
What rocks look like magnesiohulsite?+
What minerals are found with magnesiohulsite?+
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Find magnesiohulsite on the map
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