Thermessaite-(NH4) is a rare ammonium sulfate-fluoride mineral primarily found as a sublimation product in fumaroles. It typically forms small tabular crystals in association with other volcanic minerals at the La Fossa crater of Vulcano, Italy.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrare

Thermessaite-(NH4)

Hardness: 2-3
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

No image

Is this thermessaite-(nh4)?

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 thermessaite-(nh4) with a known reference. Thermessaite-(NH4) sits at Mohs 2-3, 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, white.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular crystals.

Often confused with

Thermessaite-(NH4) vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside thermessaite-(nh4)

Minerals reported to co-occur with thermessaite-(nh4). Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: (NH₄)₂AlF₃(SO₄)
Mohs hardness: 2-3
Density: 2.185 g/cm³
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Tabular crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Fumarole sublimate encrustation at the rim of an active volcanic crater

Where rockhounds find thermessaite-(nh4)

Classic worldwide localities

La Fossa crater, Vulcano, Aeolian Islands, Italy (type locality)
Burning Anna I coal dump, Anna mine, near Aachen, North Rhine-Westphalia, Germany

Field-hunting tip

Where it forms: Fumarole sublimate encrustation at the rim of an active volcanic crater. If you start seeing thermessaite, sulfur, arcanite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thermessaite-(nh4)?+

Mohs hardness is 2-3. Luster: vitreous. The streak is white. Common colors include colorless, white.

Where is thermessaite-(nh4) found?+

Notable localities include La Fossa crater, Vulcano, Aeolian Islands, Italy (type locality); Burning Anna I coal dump, Anna mine, near Aachen, North Rhine-Westphalia, Germany.

What rocks look like thermessaite-(nh4)?+

Thermessaite-(NH4) is most often confused with Hieratite, Mascagnite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with thermessaite-(nh4)?+

Thermessaite-(NH4) commonly co-occurs with Thermessaite, Sulfur, Arcanite, Mascagnite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thermessaite-(nh4) form in?+

Where it forms: Fumarole sublimate encrustation at the rim of an active volcanic crater. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thermessaite-(nh4) used for?+

Thermessaite-(NH4) is used in collector.

Find thermessaite-(nh4) on the map

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