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

mineralrare

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, 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.