Pinnoite is a rare borate mineral typically found in marine evaporite deposits as small, yellow, prismatic crystals or fibrous masses. Collectors look for its characteristic radial habits often embedded in halite or associated with other borate species like boracite.
Is this pinnoite?
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 pinnoite with a known reference. Pinnoite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow, colorless, yellow green, light yellow.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: granular, nodular, radial.
Often confused with
Pinnoite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside pinnoite
Minerals reported to co-occur with pinnoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgB₂O₄·3H₂O
- Mohs hardness
- 3.5
- Density
- 2.27 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Granular, nodular, radial
- Cleavage
- Indistinct
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- Typically in bedded marine salt deposits; an efflorescence around salt springs and lakes
Where rockhounds find pinnoite
Classic worldwide localities
- Eagle Borax Spring, Furnace Creek district, Death Valley, Inyo Co., California, USA
- Saxony-Anhalt, from the Stassfurt-Leopoldshall district, at Schmidtmannshall, near Aschersleben, Germany
- Inder borate deposit, Kazakhstan
- Da Quidam saline lake, Qinghai-Xizang Plateau, Tibet, China
- Socacastro, Salta Province, Argentina
Field-hunting tip
Where it forms: Typically in bedded marine salt deposits; an efflorescence around salt springs and lakes. If you start seeing boracite, kaliborite in float, you are in the right ground. Typical habit: granular, nodular, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pinnoite?+
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What rocks look like pinnoite?+
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Find pinnoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
