Glaucophane is a primary indicator mineral for high-pressure, low-temperature metamorphic conditions, often found in blueschist facies rocks. It typically forms long, slender prismatic or fibrous crystals with a distinctive blue or blue-grey coloration.

Hardness

Mohs

Luster

Vitreous to pearly

Streak

Blue-gray

Transparency

Translucent

mineralcommonAmphibole Group family

Glaucophane

Hardness: 6
Luster: Vitreous to pearly
Streak: Blue-gray
Transparency: Translucent

Is this glaucophane?

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 glaucophane with a known reference. Glaucophane sits at Mohs 6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: blue-gray.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to pearly.
4
Match the color range
Compare against the expected color range: blue, blue-gray, lavender, black, gray, bluish black, lavender blue, azure blue.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: columnar, granular, massive.

Often confused with

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

mineral

Riebeckite

Mohs 6

How to tell apart: Streak differs, so Glaucophane leaves blue-gray, Riebeckite leaves greenish brown.

How to tell apart: Streak differs, so Glaucophane leaves blue-gray, Actinolite leaves white.

Compare →

Often found alongside glaucophane

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

All properties

Chemical formula: Na₂(Mg₃Al₂)(Si₈O₂₂)(OH)₂
Mohs hardness: 6
Density: 3.08-3.22 g/cm³
Colors: Blue Blue-gray Lavender Black Gray Bluish blackLavender blueAzure blue
Streak: Blue-gray
Luster: Vitreous to pearly
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Columnar, granular, massive
Cleavage: Perfect on {110}, intersecting at ~56° and ~124°; partings on {010}, {001}
Rarity: Common
Uses: Collector, Geological indicator
Host rock: Characteristic of the blueschist facies, in former subduction zones in mountain belts; in the greenschist facies and in eclogites that have undergone retrograde metamorphism

Where rockhounds find glaucophane

Classic worldwide localities

Kodiak Islands, Alaska, USA
Syra Island, Cyclades Islands, Greece
St. Marcel, Val d'Aosta, and Piollore (Biella), Piedmont, Italy
Anglesey, Wales
Ubuzan, Aichi Prefecture, and Otakiyama, Tokushima Prefecture, Japan

Field-hunting tip

Where it forms: Characteristic of the blueschist facies, in former subduction zones in mountain belts; in the greenschist facies and in eclogites that have undergone retrograde metamorphism. If you start seeing crossite, chlorite, epidote in float, you are in the right ground. Typical habit: columnar, granular, massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify glaucophane?+

Mohs hardness is 6. Luster: vitreous to pearly. The streak is blue-gray. Common colors include blue, blue-gray, lavender, black.

Where is glaucophane found?+

Notable localities include Kodiak Islands, Alaska, USA; Syra Island, Cyclades Islands, Greece; St. Marcel, Val d'Aosta, and Piollore (Biella), Piedmont, Italy; Anglesey, Wales; Ubuzan, Aichi Prefecture, and Otakiyama, Tokushima Prefecture, Japan.

What rocks look like glaucophane?+

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

What minerals are found with glaucophane?+

Glaucophane commonly co-occurs with Crossite, Chlorite, Epidote, Pumpellyite, Lawsonite, Omphacite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does glaucophane form in?+

Where it forms: Characteristic of the blueschist facies, in former subduction zones in mountain belts; in the greenschist facies and in eclogites that have undergone retrograde metamorphism. Working float back to the host body is the standard way to chase a fresh occurrence.

What is glaucophane used for?+

Glaucophane is used in collector, geological indicator.

Find glaucophane on the map

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