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

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrarenull family

Hieratite

Hardness: 2
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 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Hieratite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Hieratite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, grayish.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: crusts, granular masses, small prismatic crystals.

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
Density: 2.98 g/cm³
Colors: Colorless White Grayish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Crusts, Granular Masses, Small Prismatic Crystals
Cleavage: Poor
Rarity: Rare
Uses: Collector
Host rock: Fumaroles
Typical price: $20-150 for rare specimen fragments

Where rockhounds find hieratite

Classic worldwide localities

Vesuvius, Italy
Kamchatka, Russia
Azores, Portugal
Vulcano, Italy

Field-hunting tip

Look in fumaroles country — that is the host setting where hieratite typically forms. If you start seeing malladrite, cryptohalite, sulphur in float, you are in the right ground. Field specimens usually show a crusts, granular masses, small prismatic crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hieratite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, grayish.

Where is hieratite found?+

Notable localities include Vesuvius, Italy; Kamchatka, Russia; Azores, Portugal; Vulcano, Italy.

How much is hieratite worth?+

Typical asking prices fall in the range of $20-150 for rare specimen fragments. Quality, size, and provenance can move individual specimens well outside that range.

Is hieratite safe to handle?+

It contains toxic constituents. Contains fluorine, which can be toxic if ingested or inhaled as dust; handle with care and wash hands after contact. Handle with care, avoid grinding or breathing dust, and store separately.

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 Malladrite, Cryptohalite, Sulphur, Gypsum. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hieratite form in?+

Hieratite typically forms in 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.