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Six Sided Cumengite Star Habit

The Mineral cumengeite

Cumengeite is an uncommon mineral that forms some of the most interesting crystal shapes of all minerals. Its most famous habit is as epitaxial overgrowths over Boleite, where a single specimen has an inner cubic core of Boleite, and outer protruding crystal faces of Cumengeite in triangular habit, forming a star-like formation.

Cumengeite has been found in several localities worldwide, however, its only significant source was the the Amelia Mine in Baja California, Mexico. To date, this is the only only locality that had produced this mineral in well-formed crystals of any significance.

Cumengeite is named for Edouard Cumenge (1828-1902), a French mining engineer who was among the first to collect this mineral at its type locality of Boleo, Mexico.
Chemical Formula Pb21Cu20Cl42(OH)40· 6H2O
Composition Hydroxychloride of lead and copper
Color Bright indigo blue to dark inky blue
Streak Blue
Hardness 2.5
Crystal System Tetragonal
Crystal Forms
and Aggregates
In single crystals indipyramidal habit, resembling an elongated octahedron with central cubic faces. Also in epitaxial overgrowths of pyramidal crystals on Boleite crystal faces, forming six-sided star-shaped crystal formations which may resemble a Star of David.
Transparency Translucent
Specific Gravity 4.5 - 5
Luster Vitreous, greasy
Cleavage 1,1;2,3
Fracture Conchoidal
Tenacity Brittle
In Group Halides
Striking Features Color, crystal habits, and localities
Environment In the oxidation zone deposits of copper and lead.
Rock Type Sedimentary
Popularity (1-4) 3
Prevalence (1-3) 3
Demand (1-3) 1

Cumengeite AUCTIONS

A rare collectors mineral, with good epitaxial crystals being highly valuable.

The premier locality for Cumengeite, which is also the type locality, is the Amelia mine, Santa Rosalia (Boleo), Baja California Sur, Mexico. This is the only area where Cumengeite occurs as relatively large crystals.

Boleite, Atacamite

The unique crystal formations and locality can distinguish this mineral from all other minerals.

cumengeite PHOTOS
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