Schlemaite

Chemical formula: (Cu₁+,&#₉₇₄₄;)₆(Pb₂+,Bi₃+)Se₂-₄

Schlemaite is a rare copper, lead, and bismuth selenide, forming metallic-lustered, black grains and aggregates.

## Characteristics Schlemaite is a very rare mineral from the sulfide group, specifically a selenide. It is composed of copper, lead, and bismuth. It occurs as small, anhedral (lacking its own crystal form) grains up to 200 micrometers in size. These grains often form clusters and aggregates with other selenides. Visually, it is opaque, black, and has a metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. Its hardness and density have not been precisely measured due to the small size of the grains and its rarity. It is brittle. ## History and Name The mineral's name comes from its discovery locality – the historic mining district of Schlema-Alberoda in the Ore Mountains (Erzgebirge) in Saxony, Germany. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2018 (IMA2018-079). It was described by a team of mineralogists led by Hans-Jürgen Förster.

Properties

Luster: Metallic
Streak: Black
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of schlemaite is impossible without advanced analytical techniques. Due to its occurrence as fine, black, metallic grains intergrown with other minerals, it requires analysis using an electron microscope with an EDS (energy-dispersive spectroscopy) attachment to confirm its chemical composition. Optically, it is indistinguishable from many other similar sulfides and selenides. ## Distinguishing from similar minerals Schlemaite is visually identical to many other rare selenides with which it co-occurs, such as clausthalite, umangite, klockmannite, or berzelianite. Differentiation is possible only through chemical analysis. ## Crystal forms This mineral forms exclusively anhedral grains, meaning they lack their own crystal faces, and irregular aggregates. No well-formed crystals have been observed.

Geological environment

## Genesis Schlemaite forms under hydrothermal conditions, in calcite-dolomite veins with selenide mineralization. Its formation is associated with low-temperature processes that led to the precipitation of metal selenides from solutions circulating in rock fractures. ## Mineral associations This mineral occurs in paragenesis with other selenides. It is most often accompanied by clausthalite, umangite, klockmannite, berzelianite, eukairite, tiemannite, as well as uraninite and hematite. These minerals together form complex, fine-grained aggregates. ## Localities The only confirmed locality for schlemaite worldwide is its type locality: the Schlema-Alberoda mining district in the Ore Mountains, Saxony (Germany). This is a historic area for uranium, silver, and cobalt mining, known for the occurrence of many rare minerals, including unique selenide mineralization.

Rarity

Extremely rare

For collectors

## Quality criteria As a mineral of purely scientific and systematic importance, schlemaite specimens are not subject to typical quality assessment criteria. The collector's value of a specimen depends on the richness of the mineral association and the possibility of confirming the presence of schlemaite through analysis. The most valuable samples are those where schlemaite grains are relatively large (on a micro scale) and occur in association with other rare selenides from the same locality.

Care and storage

## Cleaning Due to its extreme rarity and small grain size, schlemaite specimens are typically not cleaned. Any attempts at mechanical or chemical cleaning may damage or completely destroy the mineral. If dust removal is necessary, compressed air can be used from a safe distance. ## What to avoid Avoid contact with chemicals, acids, and ultrasonic cleaners. The mineral is brittle, so it should be protected from impacts and scratches. As a selenide, it may be susceptible to oxidation in a humid environment. ## Storage Schlemaite specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from dust, humidity, and mechanical damage. Avoid exposure to direct sunlight and extreme temperatures.

Sources

IMA Mineral List (CNMNC)