Ecdemite is a rare lead-arsenic oxychloride often found as yellow, waxy crusts or small, thin tabular crystals in oxidized zones of lead mines. Collectors look for its characteristic resinous luster and distinct color, though it is usually identified through chemical analysis due to its visual similarity to other secondary lead minerals.
Is this ecdemite?
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 ecdemite with a known reference. Ecdemite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous on cleavages, greasy on fractures.
- 4Match the color rangeCompare against the expected color range: yellow, green yellow, orange.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: encrustations, massive, tabular.
Often confused with
Ecdemite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ecdemite leaves light yellow, Mimetite leaves white; luster reads vitreous on cleavages, greasy on fractures on Ecdemite and resinous to subadamantine on Mimetite.
How to tell apart: Streak differs, so Ecdemite leaves light yellow, Wulfenite leaves white; luster reads vitreous on cleavages, greasy on fractures on Ecdemite and resinous, subadamantine to adamantine on Wulfenite.
How to tell apart: Streak differs, so Ecdemite leaves light yellow, Pyromorphite leaves white; luster reads vitreous on cleavages, greasy on fractures on Ecdemite and resinous to subadamantine on Pyromorphite.
Often found alongside ecdemite
Minerals reported to co-occur with ecdemite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₆As₂O₇Cl₄
- Mohs hardness
- 2.5-3
- Density
- 7.14 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Vitreous on cleavages, greasy on fractures
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Encrustations, massive, tabular
- Cleavage
- {001}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare mineral in metamorphosed Fe–Mn orebodies (Sweden)
Where rockhounds find ecdemite
Classic worldwide localities
- Långban, in the Harstigen mine, near Persberg, and at Jakobsberg, Värmland, Sweden
- Laurium, Greece, in slag
Field-hunting tip
Where it forms: A rare mineral in metamorphosed Fe–Mn orebodies (Sweden). If you start seeing heliophyllite, finnemanite, freedite in float, you are in the right ground. Typical habit: encrustations, massive, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find ecdemite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
