Ferrowyllieite is a rare phosphate mineral primarily found in complex granite pegmatites. It typically appears as green to yellow-green granular or crystalline masses and is often identified via chemical analysis due to its similarity to other members of the wyllieite group.
Is this ferrowyllieite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch ferrowyllieite with a known reference. Ferrowyllieite sits at Mohs >4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dirty olive-green.
- 3Read the lusterHold the specimen under a strong light. Luster: oily to submetallic.
- 4Match the color rangeCompare against the expected color range: bluish green, greenish black, gray green, dark blue green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: euhedral crystals, selvage.
Often confused with
Ferrowyllieite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferrowyllieite leaves dirty olive-green, Wyllieite leaves olive green; luster reads oily to submetallic on Ferrowyllieite and vitreous to submetallic on Wyllieite.
How to tell apart: Triplite is the harder of the two (Mohs 5-5.5 vs. >4); streak differs, so Ferrowyllieite leaves dirty olive-green, Triplite leaves white to brown; luster reads oily to submetallic on Ferrowyllieite and vitreous to resinous on Triplite.
Often found alongside ferrowyllieite
Minerals reported to co-occur with ferrowyllieite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaNaFe(FeAl)(PO₄)₃
- Mohs hardness
- >4
- Density
- 3.601 g/cm³
- Colors
- Streak
- Dirty olive-green
- Luster
- Oily to submetallic
- Transparency
- Transparent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Euhedral crystals, selvage
- Cleavage
- On {010}, perfect; on {101}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A primary phosphate in zoned granite pegmatites
Where rockhounds find ferrowyllieite
Classic worldwide localities
- Victory mine, four km northeast of Custer, Custer Co., South Dakota, and at the G.E. Smith mine, Newport, Sullivan Co., New Hampshire, USA
Field-hunting tip
Where it forms: A primary phosphate in zoned granite pegmatites. If you start seeing arrojadite, muscovite, schorl in float, you are in the right ground. Typical habit: euhedral crystals, selvage. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrowyllieite?+
Where is ferrowyllieite found?+
What rocks look like ferrowyllieite?+
What minerals are found with ferrowyllieite?+
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Find ferrowyllieite on the map
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