Tobelite is a rare ammonium-bearing mica that commonly forms in low-temperature hydrothermal environments associated with organic-rich sediments. It is often visually indistinguishable from muscovite or illite, requiring X-ray diffraction or chemical analysis for positive identification.
Is this tobelite?
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 tobelite with a known reference. Tobelite 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: silky.
- 4Match the color rangeCompare against the expected color range: yellowish green, pearly white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, scaly.
Often confused with
Tobelite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky on Tobelite and vitreous to pearly or silky on Muscovite.
How to tell apart: Luster reads silky on Tobelite and earthy on Illite.
How to tell apart: Luster reads silky on Tobelite and pearly on Paragonite.
Often found alongside tobelite
Minerals reported to co-occur with tobelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)Al₂(Si₃Al)O₁₀(OH)₂
- Mohs hardness
- 2
- Density
- 2.58-2.62 g/cm³
- Colors
- Yellowish greenPearly white
- Streak
- White
- Luster
- Silky
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Massive, scaly
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A hydrothermal alteration product of a biotite andesite dike (Tobe, Japan); in a hydrothermally altered rhyolite tu® (Horo, Japan)
Where rockhounds find tobelite
Classic worldwide localities
- Ohgidani pottery stone deposit, Tobe, Ehime Prefecture, and in the Horo pyrophyllite deposit, Toyosaka, Hiroshima Prefecture, Japan
Field-hunting tip
Where it forms: A hydrothermal alteration product of a biotite andesite dike (Tobe, Japan); in a hydrothermally altered rhyolite tu® (Horo, Japan). If you start seeing quartz, ammonium-rich mica, pyrophyllite in float, you are in the right ground. Typical habit: massive, scaly. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tobelite?+
Where is tobelite found?+
What rocks look like tobelite?+
What minerals are found with tobelite?+
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What is tobelite used for?+
Find tobelite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
