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
Color
Bright indigo blue to dark inky blue
Crystal System
Tetragonal
Crystal Habits
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.
Additional Information
Composition
Hydroxychloride of lead and copper |
In Group
Halides |
Striking Features
Color, crystal habits, and localities |
Environment
In the oxidation zone deposits of copper and lead. |
Rock Type
Sedimentary |
Uses
A rare collectors mineral, with good epitaxial crystals being highly valuable.
Noteworthy Localities
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.
Common Mineral Associations
Boleite, Atacamite
Distingushing Similar Minerals
The unique crystal formations and locality can distinguish this mineral from all other minerals.