What question did this study set out to answer?

To characterize and describe the newly discovered mineral hartkoppeite from Bavaria, Germany.

April 10, 2026

Hartkoppeite, a new mineral with a novel polyoxometalate sandwich cluster

Key Points

To characterize and describe the newly discovered mineral hartkoppeite from Bavaria, Germany.
Conducted electron probe microanalysis to determine the chemical formula.
Measured physical properties including density, hardness, and crystallography.
Analyzed crystal structure using diffraction methods.
Hartkoppeite has a complex polyoxometalate sandwich cluster structure.
It features distinct crystallographic forms with specific cleavage patterns.
The calculated density of hartkoppeite is 2.88 g·cm-3, with a Mohs hardness around 2½.

Abstract

Abstract Hartkoppeite (IMA2025-056), Ca4Mn2+Mo6+6As5+4O32 (OH) 2 (H2O) 14·5H2O, is a newly approved mineral species from the Fuchs quarry, Hartkoppe, Sailauf, Bavaria, Germany. Hartkoppeite occurs as elongated and striated tabular crystals up to about 0. 2 mm long. Tablets are flattened on 110, elongated and striated parallel to 001, and exhibit the forms 110, 1-10, and 001. The mineral is colorless and transparent with vitreous luster and white streak. The Mohs hardness is ∼2½. The mineral has brittle tenacity, stepped fracture, and three cleavages: 110 very good, 001 and 1-10 good. The measured density is 2. 88 (2) g·cm-3. The mineral is optically biaxial (+), α = 1. 692 (5), β = 1. 693 (5), γ = 1. 718 (5) (white light) ; 2Vmeas = 22 (1) °; moderate r v dispersion; nonpleochroic. Electron probe microanalysis provided the empirical formula (Ca3. 88Mn2+0. 12) Σ4. 00Mn2+1. 00Mo6+6. 01As5+3. 99O32. 38 (OH) 1. 62 (H2O) 14·K0. 38 (H2O) 4. 62. Hartkoppeite is triclinic, P-1, a = 13. 34610 (15), b = 13. 53840 (12), c 14. 3087 (2) Å, α = 71. 080 (5), β = 82. 936 (6), γ = 68. 792 (5) °, V = 2280. 00 (10) Å3, and Z = 2. The crystal structure (R1 = 0. 0478 for 6216 I 2σI reflections) contains a novel polyoxometalate sandwich cluster of formula Ca4Mn2+2 (H2O) 10Mo6+6As5+4O32 (OH) 228-.

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Cite This Study

Kampf et al. (Wed,) studied this question.

synapsesocial.com/papers/69d896046c1944d70ce0726c https://doi.org/https://doi.org/10.2138/am-2026-10210

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