Cryptohalite is a rare ammonium fluorosilicate typically found as a sublimation product around volcanic fumaroles. It occurs as small, delicate hexagonal crystals or thin crusts, often in association with other fumarolic minerals like sulfur and sal ammoniac.

Hardness

2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrarenull family

Cryptohalite

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

Is this cryptohalite?

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 cryptohalite with a known reference. Cryptohalite 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. Cryptohalite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Cryptohalite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, yellowish.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: small hexagonal crystals, crusts, or granular aggregates.

Often confused with

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

Often found alongside cryptohalite

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

All properties

Chemical formula: (NH₄)₂SiF₆
Mohs hardness: 2.5
Density: 2.04 g/cm³
Colors: Colorless White Yellowish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Hexagonal
Crystal habit: Small Hexagonal Crystals, Crusts, Or Granular Aggregates
Cleavage: Poor
Rarity: Rare
Uses: Collector
Host rock: Fumarolic Deposits
Typical price: $20-100 per specimen

Where rockhounds find cryptohalite

Classic worldwide localities

Vesuvius, Italy
Kamchatka, Russia
Tolbachik Volcano, Russia

Field-hunting tip

Look in fumarolic deposits country — that is the host setting where cryptohalite typically forms. If you start seeing sal ammoniac, realgar, sulfur in float, you are in the right ground. Field specimens usually show a small hexagonal crystals, crusts, or granular aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cryptohalite?+

Mohs hardness is 2.5. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, yellowish.

Where is cryptohalite found?+

Notable localities include Vesuvius, Italy; Kamchatka, Russia; Tolbachik Volcano, Russia.

How much is cryptohalite worth?+

Typical asking prices fall in the range of $20-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is cryptohalite safe to handle?+

It contains toxic constituents. Contains fluorine and ammonium; toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid dust generation. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like cryptohalite?+

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

What minerals are found with cryptohalite?+

Cryptohalite commonly co-occurs with Sal ammoniac, Realgar, Sulfur. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cryptohalite form in?+

Cryptohalite typically forms in fumarolic deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cryptohalite used for?+

Cryptohalite is used in collector.

Find cryptohalite on the map

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