Hieratite is a rare potassium fluorosilicate that forms as a sublimate in volcanic fumaroles. It typically occurs as white or colorless crusts and delicate crystals in high-temperature volcanic environments, often associated with other rare fluoride minerals.

Hardness

~2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Hieratite

Hardness: ~2.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this hieratite?

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 hieratite with a known reference. Hieratite sits at Mohs ~2.5, 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, gray.
5
Look at form & habit
Crystal system: cubic. Typical habit: concretionary, stalactitic.

Often confused with

Hieratite vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside hieratite

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

All properties

Chemical formula: K₂SiF₆
Mohs hardness: ~2.5
Density: 2.665 g/cm³
Colors: Colorless White Gray
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Cubic
Crystal habit: Concretionary, stalactitic
Cleavage: {111}, perfect
Rarity: Rare
Uses: Collector
Host rock: As a deposit around volcanic fumaroles

Where rockhounds find hieratite

Classic worldwide localities

Vulcano, Lipari Islands, and from Vesuvius, Campania, Italy

Field-hunting tip

Where it forms: As a deposit around volcanic fumaroles. If you start seeing sassolite, mirabilite, glauberite in float, you are in the right ground. Typical habit: concretionary, stalactitic. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hieratite?+

Mohs hardness is ~2.5. Luster: vitreous. The streak is white. Common colors include colorless, white, gray.

Where is hieratite found?+

Notable localities include Vulcano, Lipari Islands, and from Vesuvius, Campania, Italy.

Is hieratite safe to handle?+

Hieratite contains soluble fluoride. Contains fluorine, which can be toxic if ingested or inhaled as dust; handle with care and wash hands after contact.

What rocks look like hieratite?+

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

What minerals are found with hieratite?+

Hieratite commonly co-occurs with Sassolite, Mirabilite, Glauberite, Selenian sulfur, Realgar, Alums. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hieratite form in?+

Where it forms: As a deposit around volcanic fumaroles. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hieratite used for?+

Hieratite is used in collector.

Find hieratite on the map

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