Ammonioborite is a very rare ammonium borate mineral typically found as a result of fumarolic activity. It usually occurs as fragile white crusts or small, poorly defined tabular crystals in geothermal areas. Collectors generally acquire it as a micro-mineral from specific historic Italian fumarole sites.
Is this ammonioborite?
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 ammonioborite with a known reference. Ammonioborite sits at Mohs 2, 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: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crusts, aggregates of small tabular crystals.
Often confused with
Ammonioborite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside ammonioborite
Minerals reported to co-occur with ammonioborite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)₃B₁₅O₂₀(OH)₈·4H₂O
- Mohs hardness
- 2
- Density
- 1.765 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Crusts, aggregates of small tabular crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In boric acid-rich fumarolic lagoons
Where rockhounds find ammonioborite
Classic worldwide localities
- Larderello, Val di Cecina, Tuscany, Italy
Field-hunting tip
Where it forms: In boric acid-rich fumarolic lagoons. If you start seeing sassolite, larderellite in float, you are in the right ground. Typical habit: crusts, aggregates of small tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ammonioborite?+
Where is ammonioborite found?+
What rocks look like ammonioborite?+
What minerals are found with ammonioborite?+
What kind of rock does ammonioborite form in?+
What is ammonioborite used for?+
Find ammonioborite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
