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, so 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, so 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, 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
How do you identify cumengeite?+
Where is cumengeite found?+
How much is cumengeite worth?+
Is cumengeite safe to handle?+
What rocks look like cumengeite?+
What minerals are found with cumengeite?+
What kind of rock does cumengeite form in?+
What is cumengeite used for?+
Find cumengeite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
