Megacyclite is an extremely rare phyllosilicate mineral typically found in the alkaline pegmatites of the Poudrette quarry at Mont Saint-Hilaire. It is usually recognized as delicate, platy to fan-shaped crystal aggregates that are highly sensitive to dehydration.
Is this megacyclite?
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 megacyclite with a known reference. Megacyclite 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 to subvitreous.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: irregular grains.
Often confused with
Megacyclite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside megacyclite
Minerals reported to co-occur with megacyclite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KNa₈Si₉O₁₈(OH)₉·19H₂O
- Mohs hardness
- 2
- Density
- 1.82 g/cm³
- Streak
- White
- Luster
- Vitreous to subvitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Irregular grains
- Cleavage
- Perfect {100}; less perfect {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In unweathered ultra-alkalic pegmatites in an alkalic massif
Where rockhounds find megacyclite
Classic worldwide localities
- Mt. Rasvumchorr, Khibiny massif, Kola Peninsula, Russia
Field-hunting tip
Where it forms: In unweathered ultra-alkalic pegmatites in an alkalic massif. If you start seeing orthoclase, fenaksite, revdite in float, you are in the right ground. Typical habit: irregular grains. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify megacyclite?+
Where is megacyclite found?+
What rocks look like megacyclite?+
What minerals are found with megacyclite?+
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What is megacyclite used for?+
Find megacyclite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
