Lileyite is a very rare barium-rich member of the mica group found primarily in alkaline intrusive complexes. It typically appears as small tabular crystals embedded within nepheline syenite or associated alkaline rocks, often requiring micro-analysis for definitive identification due to its similarity to common biotite.

Hardness

3-4

Mohs

Streak

White

Transparency

Transparent

mineralrareMica Group family

Lileyite

Hardness: 3-4
Streak: White
Transparency: Transparent

Is this lileyite?

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 lileyite with a known reference. Lileyite sits at Mohs 3-4, 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: brown.
4
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

Often found alongside lileyite

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

All properties

Chemical formula: Ba₂Ti₂Na(NaFe)Mg(Si₂O₇)₂O₂F₂
Mohs hardness: 3-4
Density: 3.776 g/cm³
Colors: Brown
Streak: White
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular crystals
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector
Host rock: Occurs in miarolitic cavities in an alkaline basalt

Where rockhounds find lileyite

Classic worldwide localities

Löhley quarry, Üdersdorf, near Daun, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany

Field-hunting tip

Where it forms: Occurs in miarolitic cavities in an alkaline basalt. If you start seeing nepheline, leucite, augite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify lileyite?+

Mohs hardness is 3-4. The streak is white. Common colors include brown.

Where is lileyite found?+

Notable localities include Löhley quarry, Üdersdorf, near Daun, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany.

What rocks look like lileyite?+

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

What minerals are found with lileyite?+

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

What kind of rock does lileyite form in?+

Where it forms: Occurs in miarolitic cavities in an alkaline basalt. Working float back to the host body is the standard way to chase a fresh occurrence.

What is lileyite used for?+

Lileyite is used in collector.

Find lileyite on the map

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