Syngenite is a rare potassium-calcium sulfate typically found as a secondary mineral in potash evaporite deposits. Collectors often look for it as delicate prismatic crystals or white crusts associated with salt minerals, requiring careful handling due to its solubility in water.
Is this syngenite?
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 syngenite with a known reference. Syngenite sits at Mohs 2.5, 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: colorless, white, light yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, tabular, massive, crusts.
Often confused with
Syngenite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Syngenite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Luster reads vitreous on Syngenite and pearly on {010}, vitreous to greasy on {001}; vitreous on {100} on Anhydrite.
How to tell apart: Polyhalite is the harder of the two (Mohs 3.5 vs. 2.5).
Often found alongside syngenite
Minerals reported to co-occur with syngenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Ca(SO₄)₂·H₂O
- Mohs hardness
- 2.5
- Density
- 2.579-2.603 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals, tabular, massive, crusts
- Cleavage
- On {110} and {100}, perfect; on {010}, distinct
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- An uncommon diagenetic component of marine salt deposits; a volcanic sublimate or pneumatolytic reaction product; a hydrothermal vein filling in a geothermal field; derived from bat guano in caves
Where rockhounds find syngenite
Classic worldwide localities
- Haleakala volcano, Maui, Hawaii, USA
- Kalush salt deposit (Kalusz, Poland), and at Stebnyk, Ukraine
- Thuringia, in the Glückauf mine, near Sondershausen, from Bischofferode, and at Volkenroda-Pöther, near Mühlhausen, Germany
- Stassfurt salt district, Saxony-Anhalt, Germany
- Sigmundshall mine, Bokeloh, and at the Kalkberg, near Lüneburg, Lower Saxony, Germany
- Vesuvius, Campania, and in the Cesano geothermal field, Latium, Italy
Field-hunting tip
Where it forms: An uncommon diagenetic component of marine salt deposits; a volcanic sublimate or pneumatolytic reaction product; a hydrothermal vein filling in a geothermal field; derived from bat guano in caves. If you start seeing halite, arcanite, biphosphammite in float, you are in the right ground. Typical habit: prismatic crystals, tabular, massive, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify syngenite?+
Where is syngenite found?+
What rocks look like syngenite?+
What minerals are found with syngenite?+
What kind of rock does syngenite form in?+
What is syngenite used for?+
Find syngenite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
