Hillesheimite is a rare member of the zeolite group, typically occurring as delicate, fibrous, or acicular radiating clusters in volcanic basalt cavities. It is primarily recognized by its specific association with other zeolite minerals in the Eifel region of Germany.

Hardness

Mohs

Streak

White

Transparency

Transparent to translucent

mineralrareGismondine Group family

Hillesheimite

Hardness: 4
Streak: White
Transparency: Transparent to translucent

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Is this hillesheimite?

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 hillesheimite with a known reference. Hillesheimite 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, yellow, brown.
4
Look at form & habit
Crystal system: orthorhombic. Typical habit: fibrous aggregates, radiating needles.

Often confused with

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

Often found alongside hillesheimite

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

All properties

Chemical formula: (K,Ca,Ba,□)₂(Mg,Fe,Ca,□)₂[(Si,Al)₁₃O₂₃(OH)₆](OH)·8H₂O
Mohs hardness: 4
Density: 2.16 g/cm³
Colors: Colorless Yellow Brown
Streak: White
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Fibrous aggregates, radiating needles
Cleavage: Perfect on (010), less perfect on (100) and (001)
Rarity: Rare
Uses: Collector
Host rock: Encrusts the walls of miarolitic cavities in alkali basalt

Where rockhounds find hillesheimite

Classic worldwide localities

Graulai basalt quarry, near Hillesheim, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany

Field-hunting tip

Where it forms: Encrusts the walls of miarolitic cavities in alkali basalt. If you start seeing nepheline, augite, fluorapatite in float, you are in the right ground. Typical habit: fibrous aggregates, radiating needles. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hillesheimite?+

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

Where is hillesheimite found?+

Notable localities include Graulai basalt quarry, near Hillesheim, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany.

What rocks look like hillesheimite?+

Hillesheimite is most often confused with Phillipsite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with hillesheimite?+

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

What kind of rock does hillesheimite form in?+

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

What is hillesheimite used for?+

Hillesheimite is used in collector.

Find hillesheimite on the map

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