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.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Philoxenite

Hardness: ~3
Luster: Vitreous
Streak: White
Transparency: Transparent

No image

Is this philoxenite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch philoxenite with a known reference. Philoxenite sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: colorless, very pale yellowish.
5
Look at form & habit
Crystal system: triclinic. 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: (K,Na,Pb)₄(Na,Ca)₂(Mg,Cu)₃(Fe³⁺₀.₅Al₀.₅)(SO₄)₈
Mohs hardness: ~3
Density: 2.732 g/cm³
Colors: ColorlessVery pale yellowish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Tabular crystals, crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A sublimate at an active volcanic fumarole

Where rockhounds find philoxenite

Classic worldwide localities

Yadovitaya fumarole, Second scoria cone, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik Volcano, Kamchatka, Russia

Field-hunting tip

Where it forms: A sublimate at an active volcanic fumarole. If you start seeing euchlorine, langbeinite, hematite in float, you are in the right ground. Typical habit: tabular crystals, crusts. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify philoxenite?+

Mohs hardness is ~3. Luster: vitreous. The streak is white. Common colors include colorless, very pale yellowish.

Where is philoxenite found?+

Notable localities include Yadovitaya fumarole, Second scoria cone, Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik Volcano, Kamchatka, Russia.

Is philoxenite safe to handle?+

Philoxenite contains copper and lead. Contains lead, which is toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust.

What rocks look like philoxenite?+

Philoxenite is most often confused with Aphthitalite, Glauberite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with philoxenite?+

Philoxenite commonly co-occurs with Euchlorine, Langbeinite, Hematite, Tenorite, Piypite, Alumoklyuchevskite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does philoxenite form in?+

Where it forms: A sublimate at an active volcanic fumarole. Working float back to the host body is the standard way to chase a fresh occurrence.

What is philoxenite used for?+

Philoxenite is used in collector.

Find philoxenite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.