Cumengeite is a highly prized secondary mineral known for its distinctive deep indigo-blue, pseudo-cubic or pyramidal crystals. It is typically found in oxidized lead-copper deposits and is often associated with the mineral boleite, from which it is sometimes distinguished by its more elongated, star-like crystal formations.
Is this cumengeite?
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 cumengeite with a known reference. Cumengeite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Cumengeite leaves a pale blue streak.
- 3Read the lusterHold the specimen under a strong light. Cumengeite typically shows a vitreous to adamantine luster.
- 4Match the color rangeCompare against the expected color range: indigo blue, dark blue.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: pyramidal crystals, pseudo-cubic, stellate groups.
Often confused with
Cumengeite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Cumengeite leaves pale blue, Boleite leaves light blue; luster reads vitreous to adamantine on Cumengeite and vitreous on Boleite.
How to tell apart: Streak differs — Cumengeite leaves pale blue, Pseudoboleite leaves blue; luster reads vitreous to adamantine on Cumengeite and vitreous on Pseudoboleite.
Often found alongside cumengeite
Minerals reported to co-occur with cumengeite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂₁Cu₂₀Cl₄₂(OH)₄₀
- Mohs hardness
- 2.5
- Density
- 4.67 g/cm³
- Colors
- Streak
- Pale Blue
- Luster
- Vitreous to Adamantine
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Pyramidal Crystals, Pseudo-cubic, Stellate Groups
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Ore Deposits
- Typical price
- $100-2000 per specimen depending on size and quality
Where rockhounds find cumengeite
Classic worldwide localities
- Boleo District, Mexico
- Laurion, Greece
Field-hunting tip
Look in oxidized ore deposits country — that is the host setting where cumengeite typically forms. If you start seeing boleite, pseudoboleite, anglesite in float, you are in the right ground. Field specimens usually show a pyramidal crystals, pseudo-cubic, stellate groups habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find cumengeite on the map
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