Elundeid

Elundeid is a rare mineral species described in the mid-20th century. It is categorized as a metallic sulfide with a variable composition and a distinctive monoclinic crystal habit. The color ranges from pale olive-gray to steel-gray, and it has a metallic to submetallic luster. Hardness on the Mohs scale is about 5 to 6.

The name elundeid derives from the Elunda region where the mineral was first identified. The suffix -eid is used in some mineral-naming traditions to denote a mineral species.

Elundeid occurs in hydrothermally altered metamorphic rocks and skarns, often in districts with abundant manganese and iron. It is typically found as fine-grained masses or microscopic crystals in quartz veins and is commonly associated with garnet, magnetite, chlorite, and pyrite.

The chemistry is variable, with copper, iron, and sulfur forming core constituents and small amounts of arsenic, antimony, or tellurium detected in some samples. The mineral is described as having a layered or anisotropic crystal structure, contributing to distinct reflexes under polarized light.

Because elundeid lacks a fixed stoichiometry in many samples, some mineralogists consider it a distinct species, while others view it as a compositional variety of related sulfide minerals. Crystallographic studies have been used to clarify its status.

Elundeid is of interest mainly to mineralogists and collectors due to its rarity and unusual structure. Its study offers insights into hydrothermal ore formation and mineral-chemistry variability in metamorphic settings, but published data remain limited.