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

Streak

White

Transparency

Translucent

mineralcommonAmphibole Group family

Glaucophane

Hardness: 6
Luster: Vitreous
Streak: White
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. Glaucophane leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Glaucophane typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: blue, blue-gray, lavender, black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic crystals, fibrous, massive, granular.

Often confused with

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

mineral

Riebeckite

Mohs 5-6

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

How to tell apart: Luster reads vitreous on Glaucophane and vitreous to silky on Actinolite.

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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: 3.0-3.2 g/cm³
Colors: Blue Blue-gray Lavender Black
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Prismatic Crystals, Fibrous, Massive, Granular
Cleavage: Perfect On {110}
Rarity: Common
Uses: Collector, Geological Indicator
Host rock: Blueschist Metamorphic Rocks
Typical price: $5-50 for small cabinet specimens

Where rockhounds find glaucophane

Classic worldwide localities

Blueschist facies terranes
Island of Syra, Greece
Sonoma County, California, USA
Ile de Groix, France
Piedmont, Italy

Field-hunting tip

Look in blueschist metamorphic rocks country, the host setting where glaucophane typically forms. If you start seeing lawsonite, jadeite, epidote in float, you are in the right ground. Field specimens usually show a prismatic crystals, fibrous, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify glaucophane?+

Mohs hardness is 6. It typically shows a vitreous luster. The streak is white. Common colors include blue, blue-gray, lavender, black.

Where is glaucophane found?+

Notable localities include Blueschist facies terranes; Island of Syra, Greece; Sonoma County, California, USA; Ile de Groix, France; Piedmont, Italy.

How much is glaucophane worth?+

Typical asking prices fall in the range of $5-50 for small cabinet specimens. Quality, size, and provenance can move individual specimens well outside that range.

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 Lawsonite, Jadeite, Epidote, Garnet, Muscovite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does glaucophane form in?+

Glaucophane typically forms in blueschist metamorphic rocks. 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.