Roymillerite is a rare lead-magnesium silicate mineral known almost exclusively from the famous Långban mine in Sweden. It typically forms attractive, thin platy crystals with a distinct pearly luster that are highly sought after by advanced collectors of rare minerals.
Is this roymillerite?
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 roymillerite with a known reference. Roymillerite sits at Mohs ~3, 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: colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy crystals.
Often confused with
Roymillerite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Manganhumite is the harder of the two (Mohs 4 vs. ~3); luster reads vitreous on Roymillerite and subadamantine on Manganhumite.
How to tell apart: Katoptrite is the harder of the two (Mohs 5.5 vs. ~3); streak differs, so Roymillerite leaves white, Katoptrite leaves red brown; luster reads vitreous on Roymillerite and metallic, brilliant on Katoptrite.
Often found alongside roymillerite
Minerals reported to co-occur with roymillerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂₄Mg₉(Si₁₀O₂₈)(CO₃)₁₀(BO₃)(SiO₄)(OH)₁₃O₅
- Mohs hardness
- ~3
- Density
- 5.973 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Platy crystals
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In locally Pb-Cu-rich, non-sulfide portions of an Fe-Mn oxide deposit
Where rockhounds find roymillerite
Classic worldwide localities
- Kombat mine, Otavi Valley, 49 km south of Tsumeb, Grootfontein district, Otjozondjupa region, northern Namibia
Field-hunting tip
Where it forms: In locally Pb-Cu-rich, non-sulfide portions of an Fe-Mn oxide deposit. If you start seeing rhodochrosite, cerussite, jacobsite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify roymillerite?+
Where is roymillerite found?+
Is roymillerite safe to handle?+
What rocks look like roymillerite?+
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Find roymillerite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
