Year: 2025
Type: article
Abstract: The new mineral almagreraite (IMA2025-025), Cu 2+ ZnMn 4+ 3 O 8 , was found on the dump of the República Romana mine, Sierra Almagrera, Cuevas del Almanzora, Almería, Andalusia, Spain, where it occurs as tapering prisms or blades up to ∼0.4 mm in length, commonly forming subparallel to divergent aggregates. It is a secondary mineral associated intimately with well-crystallized blades of malachite on a matrix consisting of well-crystallized goethite and massive friable hematite. Crystals are black and opaque with submetallic lustre. The streak is dark grey with a brownish tint. The tenacity is brittle and the fracture is splintery. There are probably two cleavages (possibly {100} and {010}). The Mohs hardness is ∼5. The calculated density is 5.174 g·cm –3 based upon the empirical formula. In reflected light, the mineral is bluish grey in colour with moderate bireflectance and slightly bluish grey to a lighter bluish grey pleochroism. Electron probe microanalyses provided (Mn 4+ 3.05 Cu 2+ 0.93 Zn 0.91 Al 0.05 ) Σ4.94 O 8 . Almagreraite is orthorhombic, Pmn 2 1 , a = 5.7298(4), b = 4.9715(4), c = 9.3479(7) Å, V = 266.28(3) Å 3 and Z = 2. In the crystal structure ( R 1 = 0.0297 for 423 I > 2σ I reflections), Mn 4+ O 6 octahedra share edges forming an octahedral sheet parallel to {001}. One in every four octahedra in the sheet is vacant, providing the sheet formula [Mn 4+ 3 O 8 ] 4– . Successive sheets are connected via bonds to Cu 2+ and Zn 2+ located in a layer between the sheets. The structure is similar to that of minerals of the nolanite supergroup and most notably the kamiokite group. Almagreraite is a member of a family of mixed-metal oxides with the generic formula M 2 Mn 3 O 8 , which are an important subject of study for the development of new materials.
Source: Mineralogical Magazine
Authors: Anthony R. Kampf, Georges Favreau, Chi Ma, Chris Stanley
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W7115693406