Fishtail Selenite refers to the cyclic contact twinning of gypsum crystals that form distinct V-shaped or 'fishtail' morphologies. These crystals are highly fragile and prized by collectors for their geometric symmetry and excellent transparency, often found in clay-rich evaporite deposits.
Is this fishtail selenite?
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 fishtail selenite with a known reference. Fishtail Selenite 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. Fishtail Selenite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fishtail Selenite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellowish, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: twinned prismatic crystals with a characteristic V-shape.
Often confused with
Fishtail Selenite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Anhydrite is the harder of the two (Mohs 3.5 vs. 2); luster reads pearly on Fishtail Selenite and vitreous on Anhydrite.
How to tell apart: Calcite is the harder of the two (Mohs 3 vs. 2); luster reads pearly on Fishtail Selenite and vitreous on Calcite.
How to tell apart: Celestite is the harder of the two (Mohs 3-3.5 vs. 2); luster reads pearly on Fishtail Selenite and vitreous on Celestite.
Often found alongside fishtail selenite
Minerals reported to co-occur with fishtail selenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaSO₄·2H₂O
- Mohs hardness
- 2
- Density
- 2.31-2.33 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Twinned Prismatic Crystals with A Characteristic V-shape
- Cleavage
- Perfect in One Direction
- Fluorescence
- Often Fluorescent White or Yellow Under SW and LW UV
- Rarity
- Common
- Uses
- Collector, Decorative
- Host rock
- Evaporite Deposits and Clay Beds
- Typical price
- $5-50 for small specimens, $100+ for large museum-grade clusters
Where rockhounds find fishtail selenite
Classic worldwide localities
- Naica Mine, Mexico
- Red River Floodway, Canada
- Oklahoma, USA
- Lubin, Poland
Field-hunting tip
Look in evaporite deposits and clay beds country — that is the host setting where fishtail selenite typically forms. If you start seeing calcite, aragonite, sulfur in float, you are in the right ground. Field specimens usually show a twinned prismatic crystals with a characteristic v-shape habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fishtail selenite?+
Where is fishtail selenite found?+
How much is fishtail selenite worth?+
What rocks look like fishtail selenite?+
What minerals are found with fishtail selenite?+
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Find fishtail selenite on the map
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