Masutomilite is a rare manganese-rich lithium mica that is primarily sought after by advanced collectors of rare pegmatite minerals. It is typically found in small, delicate tabular crystals or platy aggregates, frequently occurring in lithium-bearing granite pegmatites associated with other rare silicate minerals.
Is this masutomilite?
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 masutomilite with a known reference. Masutomilite sits at Mohs 2.5, 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 to pearly.
- 4Match the color rangeCompare against the expected color range: purple pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: pseudo hexagonal.
Often confused with
Masutomilite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to pearly on Masutomilite and pearly to vitreous on Lepidolite.
How to tell apart: Luster reads vitreous to pearly on Masutomilite and pearly to waxy when fine-grained on Polylithionite.
Often found alongside masutomilite
Minerals reported to co-occur with masutomilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KLiAlMn(AlSi₃O₁₀)(F,OH)₂
- Mohs hardness
- 2.5
- Density
- 2.90-2.94 g/cm³
- Colors
- Purple pink
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Pseudo hexagonal
- Cleavage
- {001}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a druse in a granite pegmatite, as the core of a crystal zoned with manganoan zinnwaldite (Tanakamiyama, Japan)
Where rockhounds find masutomilite
Classic worldwide localities
- Washington Pass, Okanogan Co., Washington, USA
- Tanakamiyama, Otsu, Shiga Prefecture, and Tawara, Gifu Prefecture, Japan
- Ctidružice, Czech Republic
Field-hunting tip
Where it forms: In a druse in a granite pegmatite, as the core of a crystal zoned with manganoan zinnwaldite (Tanakamiyama, Japan). If you start seeing zinnwaldite, topaz, tourmaline in float, you are in the right ground. Typical habit: pseudo hexagonal. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify masutomilite?+
Where is masutomilite found?+
What rocks look like masutomilite?+
What minerals are found with masutomilite?+
What kind of rock does masutomilite form in?+
What is masutomilite used for?+
Find masutomilite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
