Therasiaite is an extremely rare ammonium sulfate mineral first discovered in the volcanic fumaroles of Therasia Island, Greece. It typically occurs as small, delicate, colorless to white tabular crystals forming within sulfurous volcanic vent environments.
Is this therasiaite?
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 therasiaite with a known reference. Therasiaite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Therasiaite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Therasiaite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals.
Often confused with
Therasiaite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside therasiaite
Minerals reported to co-occur with therasiaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)₃Na(SO₄)₂
- Mohs hardness
- 3.5
- Density
- 2.42 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals
- Cleavage
- Distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Fumarolic Deposits
- Typical price
- n/a
Where rockhounds find therasiaite
Classic worldwide localities
- Therasia, Santorini, Greece
Field-hunting tip
Look in fumarolic deposits country — that is the host setting where therasiaite typically forms. If you start seeing gypsum, alunite, sulfur in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find therasiaite on the map
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