Lemanskiite

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Lemanskiite specimen - rock identification

What is Lemanskiite?

Lemanskiite is a mineral that was first discovered in a mine at Abundancia mine, El Guanaco mining district, Chile, with the ideal formula of NaCaCu5(AsO4)4Cl•3H2O. Originally, this mineral was discovered as being dimorphus with lavendulan, but in 2018 it was revised to only have 3 water molecules. Lemanskiite typically occurs as rosette-shaped aggregates of thin lamellar or needle-shaped aggregates, such as lammerite. Lemanskiite is dark sky blue with a light blue streak, it is brittle with an excellent cleavage plane. It was found on a dumping site in the abandoned Abundancia mine, El Guanaco mining district, Region II, Antofagasta Province, Chile The new mineral has been named after Chester S. Lemanski, Jr. This mineral and name were then approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.

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North ZoneCentral RidgeSouth Basin

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Key Characteristics

Characteristics of Lemanskiite

Lemanskiite normally forms with a habit of very large nodules up to five centimeters long; it can also form with veins of quartz. Lemanskiite has two different types of occurrences, needle-shaped and rosette-shaped aggregates. The needle-shaped aggregates are very thin plate-like individual crystals with a length of 0.8mm and have a thickness of 10 μm. The rosette-shaped aggregates are thin, lamellar, subparallel intergrowths with very thin individual domains. Lemanskiite comes in a dark sky blue color. The mineral has also been found to be translucent. Lemanskiite has a hardness of approx. 2.5 on the Mohs scale, and has a density of 3.78g/cm. It has excellent cleavage parallel to the largest face visible which is (001), has a brittle tenacity, has a light blue streak, and has a vitreous luster.

Composition of Lemanskiite

Lemanskiite is a member of the lavendulan group, and has a crystal structure that is based on heteropolyhedral layers parallel to (100). The heteropolyherdal layer are represented as Cu-centered polyhedra and AsO4 tetrahedra. This new structural type being formed, shows clusters of four-edge shared copper fivefold polyhedra forming distorted tetragonal pyramids, with a chlorine being the shared apex. However, even though lemanskiite is a member of the lavendulan group, it differs in that the fourth vertex in each of the AsO4 is linked a copper-centered without a copper fivefold polyhedra cluster. Due to this, this copper site is instead a centered tetragonal pyramid with the oxygen atom of water molecule at a distant fifth apex CuO4(H2O).

Quick Facts

Physical Properties

Color
Sky Blue
Hardness (Mohs)
2 - 3
Density
3.86 g/cm³
Streak
Sky blue

Chemical Properties

Chemical Formula
NaCaCu5(AsO4)4Cl · 3H2O Originally thought to have 5 waters, and therefore to be a polymorph of lavendulan, but revised to 3 waters by Zubkova et al., 2018.
Elements
As, Ca, Cl, Cu, H, Na, O
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