Gypsum is a soft sulfate mineral commonly found in evaporite sedimentary environments. It is easily identified by its extremely low hardness and ability to form long, transparent bladed crystals known as Selenite, or massive, fine-grained deposits known as Alabaster.
Is this gypsum?
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 gypsum with a known reference. Gypsum 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. Gypsum leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Gypsum typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray, yellow, honey.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, prismatic, bladed, fibrous.
Often confused with
Gypsum 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).
How to tell apart: Calcite is the harder of the two (Mohs 3 vs. 2).
How to tell apart: Gypsum is noticeably harder (Mohs 2 vs. 1); luster reads vitreous on Gypsum and pearly on Talc.
Often found alongside gypsum
Minerals reported to co-occur with gypsum. 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
- 2.3 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Prismatic, Bladed, Fibrous
- Cleavage
- Perfect in One Direction
- Fluorescence
- Often Fluorescent White or Yellow Under LW UV
- Rarity
- Common
- Uses
- Collector, Decorative, Industrial
- Host rock
- Evaporite Deposits, Sedimentary Basins
- Typical price
- $5-50 for small specimens, $100+ for large display crystals
Where rockhounds find gypsum
56 mapped spotsClassic worldwide localities
- Naica Mine, Mexico
- White Sands, New Mexico, USA
- Red River, Manitoba, Canada
- Maras, Peru
- Morocco
U.S. states with gypsum
Each link opens a state-specific list of mapped rockhounding spots that produce gypsum.
Field-hunting tip
Look in evaporite deposits, sedimentary basins country — that is the host setting where gypsum typically forms. If you start seeing halite, calcite, sulfur in float, you are in the right ground. Field specimens usually show a tabular crystals, prismatic, bladed, fibrous habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, Wyoming, Missouri — start trip planning there.
Common questions
How do you identify gypsum?+
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Find gypsum on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
