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Wyllieite is a rare phosphate mineral typically found as a primary or secondary phase in complex granite pegmatites. It is often identified by its distinct green to brownish hues and its occurrence alongside other phosphate minerals like triphylite. Collectors generally look for it in classic pegmatite localities where it forms small, well-defined prismatic crystals or massive aggregates.

Hardness
4-4.5
Mohs
Luster
Vitreous to submetallic
Streak
Olive green
Transparency
Semitransparent

Is this wyllieite?

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 wyllieite with a known reference. Wyllieite sits at Mohs 4-4.5, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: olive green.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: vitreous to submetallic.
  • 4
    Match the color range
    Compare against the expected color range: dark green, bluish green, greenish black, gray green.
  • 5
    Look at form & habit
    Crystal system: monoclinic. Typical habit: prismatic crystals, massive, granular.

Often confused with

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

Fairfieldite mineral
mineral
Fairfieldite
Mohs 3.5

How to tell apart: Streak differs, so Wyllieite leaves olive green, Fairfieldite leaves white; luster reads vitreous to submetallic on Wyllieite and pearly to subadamantine, vitreous on the {001} cleavage on Fairfieldite.

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Often found alongside wyllieite

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

All properties

Chemical formula
Na₂Mn²⁺(Fe²⁺,Fe³⁺)Al(PO₄)₃
Mohs hardness
4-4.5
Density
3.601 g/cm³
Colors
Dark greenBluish greenGreenish blackGray green
Streak
Olive green
Luster
Vitreous to submetallic
Transparency
Semitransparent
Crystal system
Monoclinic
Crystal habit
Prismatic crystals, massive, granular
Cleavage
None
Rarity
Rare
Uses
Collector
Host rock
In zoned complex granite pegmatites

Where rockhounds find wyllieite

Classic worldwide localities

  • Old Mike mine, six km north-northwest of Custer, Custer Co., South Dakota, USA
  • Buranga pegmatite, near Gatumba, Rwanda
  • Hålsjöberg, Värmland, Sweden
  • Lavra do Énio pegmatite, northeast of Galiléia, Minas Gerais, Brazil

Field-hunting tip

Where it forms: In zoned complex granite pegmatites. If you start seeing trolleite, scorzalite in float, you are in the right ground. Typical habit: prismatic crystals, massive, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify wyllieite?+
Mohs hardness is 4-4.5. Luster: vitreous to submetallic. The streak is olive green. Common colors include dark green, bluish green, greenish black, gray green.
Where is wyllieite found?+
Notable localities include Old Mike mine, six km north-northwest of Custer, Custer Co., South Dakota, USA; Buranga pegmatite, near Gatumba, Rwanda; Hålsjöberg, Värmland, Sweden; Lavra do Énio pegmatite, northeast of Galiléia, Minas Gerais, Brazil.
What rocks look like wyllieite?+
Wyllieite is most often confused with Fairfieldite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with wyllieite?+
Wyllieite commonly co-occurs with Trolleite, Scorzalite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does wyllieite form in?+
Where it forms: In zoned complex granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.
What is wyllieite used for?+
Wyllieite is used in collector.

Find wyllieite on the map

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