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 5.5-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark brown.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, aggregates, microscopic crystals.
Often confused with
Magnesiohulsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Magnesiohulsite is noticeably harder (Mohs 5.5-6.5 vs. ~3); streak differs, so Magnesiohulsite leaves dark brown, Hulsite leaves black.
How to tell apart: Streak differs, so Magnesiohulsite leaves dark brown, Ludwigite leaves black to greenish black.
How to tell apart: Streak differs, so Magnesiohulsite leaves dark brown, Vonsenite leaves brownish black; luster reads submetallic on Magnesiohulsite and metallic to submetallic, silky if fibrous on Vonsenite.
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
- Mg₂FeO₂(BO₃)
- Mohs hardness
- 5.5-6.5
- Density
- 4.18 g/cm³
- Colors
- Streak
- Dark brown
- Luster
- Submetallic
- Transparency
- Opaque, transparent in thin section
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, aggregates, microscopic crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a magnesium skarn borate deposit at the contact between granite and calcite–dolomite rocks
Where rockhounds find magnesiohulsite
Classic worldwide localities
- Daiy Mountain, Qiliping, Changning Co., Hunan Province, China
Field-hunting tip
Where it forms: In a magnesium skarn borate deposit at the contact between granite and calcite–dolomite rocks. If you start seeing szaibélyite, kotoite, fluoborite in float, you are in the right ground. Typical habit: acicular, aggregates, microscopic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesiohulsite?+
Where is magnesiohulsite found?+
What rocks look like magnesiohulsite?+
What minerals are found with magnesiohulsite?+
What kind of rock does magnesiohulsite form in?+
What is magnesiohulsite used for?+
Find magnesiohulsite on the map
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