Eudidymite is a rare beryllium silicate that often forms distinct pseudo-hexagonal, tabular crystals. It is chemically dimorphous with epididymite and is primarily found as a late-stage mineral in alkaline pegmatites, frequently appearing as white, bladed aggregates.
Is this eudidymite?
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 eudidymite with a known reference. Eudidymite sits at Mohs 6, 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, pearly on cleavage.
- 4Match the color rangeCompare against the expected color range: blue, colorless, violet, gray, yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular, twinning common.
Often confused with
Eudidymite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside eudidymite
Minerals reported to co-occur with eudidymite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Be₂Si₆O₁₅·H₂O
- Mohs hardness
- 6
- Density
- 2.55 g/cm³
- Streak
- White
- Luster
- Vitreous, pearly on cleavage
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular, twinning common
- Cleavage
- Perfect on {001}, imperfect on {551}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage mineral in alkalic nepheline syenite pegmatites
Where rockhounds find eudidymite
Classic worldwide localities
- Arø Island, in the Langesundsfjord, Norway
- Meldon, Okehampton, Devon, England
- Věžná, Czech Republic
- Mt. Alluaiv, Lovozero massif, and Mt. Yukspor, Khibiny massif, Kola Peninsula, Russia
- Burpala massif, 120 km north of Lake Baikal, eastern Siberia, Russia
- Seal Lake, Labrador, Newfoundland, and at Mont Saint-Hilaire, Quebec, Canada
Field-hunting tip
Where it forms: A late-stage mineral in alkalic nepheline syenite pegmatites. If you start seeing albite, neptunite, aegirine in float, you are in the right ground. Typical habit: tabular, twinning common. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify eudidymite?+
Where is eudidymite found?+
Is eudidymite safe to handle?+
What rocks look like eudidymite?+
What minerals are found with eudidymite?+
What kind of rock does eudidymite form in?+
What is eudidymite used for?+
Find eudidymite on the map
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