Epididymite is a rare beryllium silicate mineral that typically forms white, thin tabular or platy crystals. It is most famously found in the alkaline pegmatites of Mont Saint-Hilaire, where it is often associated with other rare beryllium species and zeolites. It is dimorphous with eudidymite, and distinguishing between the two often requires laboratory testing or precise crystallographic analysis.
Is this epididymite?
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 epididymite with a known reference. Epididymite sits at Mohs 5.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Epididymite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Epididymite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, platy, radiating aggregates.
Often confused with
Epididymite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside epididymite
Minerals reported to co-occur with epididymite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaBeSi₃O₇(OH)
- Mohs hardness
- 5.5
- Density
- 2.54 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Platy, Radiating Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Nepheline Syenite Pegmatites
- Typical price
- $20-150 thumbnail specimens
Where rockhounds find epididymite
Classic worldwide localities
- Mont Saint-Hilaire, Canada
- Narssârssuk, Greenland
- Lovozero Massif, Russia
- Kola Peninsula, Russia
Field-hunting tip
Look in nepheline syenite pegmatites country — that is the host setting where epididymite typically forms. If you start seeing eudidymite, aegirine, microcline in float, you are in the right ground. Field specimens usually show a tabular crystals, platy, radiating aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify epididymite?+
Where is epididymite found?+
How much is epididymite worth?+
What rocks look like epididymite?+
What minerals are found with epididymite?+
What kind of rock does epididymite form in?+
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Find epididymite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
