Günterblassite is a rare phyllosilicate mineral discovered in the volcanic regions of the Eifel mountains in Germany. It typically forms thin, platy, pseudo-hexagonal crystals within the cavities of phonolitic rocks, often requiring magnification for clear identification.

Hardness

Mohs

Streak

White

Transparency

Transparent

mineralrarePhyllosilicate family

Günterblassite

Hardness: 4
Streak: White
Transparency: Transparent

Is this günterblassite?

4-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 günterblassite with a known reference. Günterblassite sits at Mohs 4, 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
Match the color range
Compare against the expected color range: colorless, pale yellow, brown.
4
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy crystals, pseudo-hexagonal aggregates.

Often found alongside günterblassite

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

All properties

Chemical formula: (K,Ca,Ba,Na,□)₃Fe[(Si,Al)₁₃O₂₅(OH,O)₄]·7H₂O
Mohs hardness: 4
Density: 2.18 g/cm³
Colors: Colorless Pale yellow Brown
Streak: White
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Platy crystals, pseudo-hexagonal aggregates
Cleavage: Perfect on (001), less perfect on (100) and (010)
Rarity: Rare
Uses: Collector
Host rock: Encrusts the walls of miaroles in alkali basalt

Where rockhounds find günterblassite

Classic worldwide localities

Mount Rother Kopf, near Gerolstein, Rheinland-Pfalz, Germany

Field-hunting tip

Where it forms: Encrusts the walls of miaroles in alkali basalt. If you start seeing nepheline, leucite, augite in float, you are in the right ground. Typical habit: platy crystals, pseudo-hexagonal aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify günterblassite?+

Mohs hardness is 4. The streak is white. Common colors include colorless, pale yellow, brown.

Where is günterblassite found?+

Notable localities include Mount Rother Kopf, near Gerolstein, Rheinland-Pfalz, Germany.

What minerals are found with günterblassite?+

Günterblassite commonly co-occurs with Nepheline, Leucite, Augite, Phlogopite, Åkermanite, Magnetite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does günterblassite form in?+

Where it forms: Encrusts the walls of miaroles in alkali basalt. Working float back to the host body is the standard way to chase a fresh occurrence.

What is günterblassite used for?+

Günterblassite is used in collector.

Find günterblassite on the map

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