Proto-anthophyllite is a rare magnesium-rich orthorhombic amphibole that is the high-temperature polymorph of the anthophyllite series. It typically occurs as small prismatic crystals or fibrous aggregates in magnesium-rich metamorphic rocks and can be very difficult to distinguish from common anthophyllite without specialized XRD analysis.

Hardness

5.5-6

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrareAmphibole Group family

Proto-anthophyllite

Hardness: 5.5-6
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this proto-anthophyllite?

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 proto-anthophyllite with a known reference. Proto-anthophyllite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Proto-anthophyllite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Proto-anthophyllite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: gray, brown, green, white.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic crystals, fibrous, lamellar.

Often confused with

Proto-anthophyllite vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside proto-anthophyllite

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

All properties

Chemical formula: Mg₂Mg₅Si₈O₂₂(OH)₂
Mohs hardness: 5.5-6
Density: 3.1-3.3 g/cm³
Colors: Gray Brown Green White
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Prismatic Crystals, Fibrous, Lamellar
Cleavage: Perfect in Two Directions
Rarity: Rare
Uses: Collector
Host rock: Metamorphic Rocks of Amphibolite Facies
Typical price: $20-150 for small specimens

Where rockhounds find proto-anthophyllite

Classic worldwide localities

Bamble, Norway
Kola Peninsula, Russia
Omi, Japan
Madagascar

Field-hunting tip

Look in metamorphic rocks of amphibolite facies country — that is the host setting where proto-anthophyllite typically forms. If you start seeing talc, olivine, serpentine in float, you are in the right ground. Field specimens usually show a prismatic crystals, fibrous, lamellar habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify proto-anthophyllite?+

Mohs hardness is 5.5-6. It typically shows a vitreous luster. The streak is white. Common colors include gray, brown, green, white.

Where is proto-anthophyllite found?+

Notable localities include Bamble, Norway; Kola Peninsula, Russia; Omi, Japan; Madagascar.

How much is proto-anthophyllite worth?+

Typical asking prices fall in the range of $20-150 for small specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is proto-anthophyllite safe to handle?+

It contains toxic constituents. Asbestiform varieties may contain hazardous microscopic fibers that pose a significant inhalation risk; handle with extreme caution and minimize dust creation. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like proto-anthophyllite?+

Proto-anthophyllite is most often confused with Anthophyllite, Cummingtonite, Tremolite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with proto-anthophyllite?+

Proto-anthophyllite commonly co-occurs with Talc, Olivine, Serpentine, Magnetite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does proto-anthophyllite form in?+

Proto-anthophyllite typically forms in metamorphic rocks of amphibolite facies. Working float back to the host body is the standard way to chase a fresh occurrence.

What is proto-anthophyllite used for?+

Proto-anthophyllite is used in collector.

Find proto-anthophyllite on the map

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