Ludlamite is a highly sought-after secondary phosphate mineral known for its vibrant green, often translucent, tabular crystals. It typically occurs as well-defined, fan-shaped aggregates or intergrown crystals in phosphate-rich hydrothermal veins. Collectors prize specimens for their distinct color and geometric crystalline beauty.
Is this ludlamite?
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 ludlamite with a known reference. Ludlamite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale greenish white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, pearly on {001} cleavage.
- 4Match the color rangeCompare against the expected color range: light green, apple green, colorless, green, greenish white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Ludlamite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Ludlamite is noticeably harder (Mohs 3.5 vs. 1.5-2); streak differs, so Ludlamite leaves pale greenish white, Vivianite leaves white, altering to dark blue, brown.
How to tell apart: Variscite is the harder of the two (Mohs 4.5 vs. 3.5); streak differs, so Ludlamite leaves pale greenish white, Variscite leaves white.
Often found alongside ludlamite
Minerals reported to co-occur with ludlamite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂²⁺Fe²⁺(PO₄)₂·4H₂O
- Mohs hardness
- 3.5
- Density
- 3.12-3.19 g/cm³
- Streak
- Pale greenish white
- Luster
- Vitreous, pearly on {001} cleavage
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- {001}, perfect; {100}, indistinct
- Rarity
- Rare
- Uses
- Collector, Specimen
- Host rock
- In complex granite pegmatites, a common hydrothermal alteration product of earlier phosphates, formed under reducing conditions
Where rockhounds find ludlamite
Classic worldwide localities
- Palermo #1 mine, North Groton, Grafton Co., New Hampshire, USA
- Blackbird mine, Lemhi Co., Idaho, USA
- Dan Patch, Ferguson, Big Chief, and other pegmatites, near Keystone, Pennington Co., South Dakota, USA
- Wheal Jane, Kea, Cornwall, England
- Hagendorf, Bavaria, Germany
- Stari Trg mine (Trepča), Kosovo, Serbia
Field-hunting tip
Where it forms: In complex granite pegmatites, a common hydrothermal alteration product of earlier phosphates, formed under reducing conditions. If you start seeing phosphoferrite, triploidite, triplite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find ludlamite on the map
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