Philoxenite is a very rare sulfate mineral found primarily in volcanic fumarole deposits, specifically at Mount Vesuvius. It typically forms as small, clear to yellowish tabular crystals or crusts that are highly sensitive to moisture and water-soluble, requiring careful storage for collectors.
Is this philoxenite?
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 philoxenite with a known reference. Philoxenite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Philoxenite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Philoxenite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, crusts.
Often confused with
Philoxenite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside philoxenite
Minerals reported to co-occur with philoxenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂NaCa₂(SO₄)₃F
- Mohs hardness
- 3
- Density
- 2.7-2.8 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Volcanic Fumaroles
- Typical price
- $50-300 per specimen
Where rockhounds find philoxenite
Classic worldwide localities
- Mount Vesuvius, Italy
Field-hunting tip
Look in volcanic fumaroles country — that is the host setting where philoxenite typically forms. If you start seeing aphthitalite, thenardite, sylvite in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify philoxenite?+
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What rocks look like philoxenite?+
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Find philoxenite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
