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.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Megacyclite

Hardness: 3
Luster: Vitreous
Streak: White
Transparency: Transparent

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Is this megacyclite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch megacyclite with a known reference. Megacyclite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Megacyclite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Megacyclite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals, radial aggregates.

Often confused with

Megacyclite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Magadiite

Mohs 1-2

How to tell apart: Megacyclite is noticeably harder (Mohs 3 vs. 1-2); luster reads vitreous on Megacyclite and pearly on Magadiite.

How to tell apart: Luster reads vitreous on Megacyclite and pearly on Kenyaite.

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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: KNaSi₉O₁₈(OH)₉·19H₂O
Mohs hardness: 3
Density: 2.28 g/cm³
Colors: White Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Platy Crystals, Radial Aggregates
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Alkaline Igneous Rocks (nepheline Syenite Pegmatites)
Typical price: $50-300 per specimen

Where rockhounds find megacyclite

Classic worldwide localities

Mont Saint-Hilaire, Quebec, Canada

Field-hunting tip

Look in alkaline igneous rocks (nepheline syenite pegmatites) country — that is the host setting where megacyclite typically forms. If you start seeing serandite, pectolite, aegirine in float, you are in the right ground. Field specimens usually show a platy crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify megacyclite?+

Mohs hardness is 3. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless.

Where is megacyclite found?+

Notable localities include Mont Saint-Hilaire, Quebec, Canada.

How much is megacyclite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like megacyclite?+

Megacyclite is most often confused with Magadiite, Kenyaite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with megacyclite?+

Megacyclite commonly co-occurs with serandite, pectolite, aegirine, microcline. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does megacyclite form in?+

Megacyclite typically forms in alkaline igneous rocks (nepheline syenite pegmatites). Working float back to the host body is the standard way to chase a fresh occurrence.

What is megacyclite used for?+

Megacyclite is used in collector.

Find megacyclite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.