Genthelvite is a rare zinc-beryllium sulfide member of the helvite group, often appearing as distinct, sharp tetrahedral crystals. It is most commonly found in highly evolved alkaline igneous complexes where it forms within cavities or veins alongside other rare minerals.
Is this genthelvite?
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 genthelvite with a known reference. Genthelvite sits at Mohs 6.5, 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: blue green, brown, colorless, green, yellow.
- 5Look at form & habitCrystal system: cubic. Typical habit: tetrahedral crystals, massive, granular.
Often confused with
Genthelvite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside genthelvite
Minerals reported to co-occur with genthelvite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₄Be₃(SiO₄)₃S
- Mohs hardness
- 6.5
- Density
- 3.44-3.70 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Cubic
- Crystal habit
- Tetrahedral crystals, massive, granular
- Cleavage
- Poor on {111}, {111}
- Fluorescence
- Green under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In miarolitic cavities in granite pegmatites; in alkaline granites and syenites, greisens, and skarns
Where rockhounds find genthelvite
Classic worldwide localities
- West Cheyenne Cañon, near St. Peters Dome, El Paso Co., Colorado, and Cumberland, Providence Co., Rhode Island, USA
- Mont Saint-Hilaire, Quebec, Canada
- Lågendalen, Tvedalen, Brevik, and on Låven Island, in the Langesundsfjord area, Norway
- Treburland mine, Altarnun, Cornwall, England
- Coire an Lochain, Cairngorm Mountains, Banffshire, Scotland
- Jos-Bukuru complex, Nigeria
Field-hunting tip
Where it forms: In miarolitic cavities in granite pegmatites; in alkaline granites and syenites, greisens, and skarns. If you start seeing phenakite, bertrandite, hambergite in float, you are in the right ground. Typical habit: tetrahedral crystals, massive, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify genthelvite?+
Where is genthelvite found?+
Is genthelvite safe to handle?+
What rocks look like genthelvite?+
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Find genthelvite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
