Yamhamelachite, KCrP₂O₇, a new natural pyrophosphate from phosphide-bearing breccia of the Hatrurim Complex, Negev Desert, Israel

Phosphide-bearing diopside-anorthite paralava found in the distribution area of the pyrometamorphic rocks of the Hatrurim Complex in Jordan (Daba-Siwaqa field) and Israel (Hatrurim Basin field) have yielded a large number of new phosphides and phosphates. In 2019, a small outcrop of phosphide-bearing breccia with cement composed of gehlenite-flamite paralava was discovered in the Hatrurim Basin. A new pyrophosphate, yamhamelachite, KCrP₂O₇ (P2₁/c, a = 7.3574(3), b = 9.9336(4), c = 8.1540(4) Å, β = 106.712(5)°, V = 570.77(5)ų, Z = 4), occurs at the phosphide-enriched boundary between an altered sedimentary xenolith and the gehlenite-flamite paralava. Yamhamelachite forms green aggregates in which the size of grains does not exceed 25-30 μm. The mineral is transparent with a glassy lustre. Yamhamelachite is brittle with conchoidal fracture. Mohs hardness = 4. The empirical formula of yamhamelachite calculated on the basis of average microprobe analyses is (K_0.89Ca_0.010.10)_∑1.00 Cr³⁺_0.50V³⁺_0.33Al_0.15Fe³⁺_0.04 Ti⁴⁺_0.03)_∑1.05P_1.98O₇. The density calculated from the empirical formula and structural data is 3.035 g·cm^-3. Cr³⁺ in yamhamelachite is substituted by V³⁺, and in a few cases V is marginally more abundant than Cr, indicating the presence of a potentially new mineral with the formula KVP₂O₇. Yamhamelachite consists of layers of Cr³⁺-octahedra and pyrophosphate groups connected at their apices, and potassium located within channels parallel to [001]. A characteristic feature of phosphide aggregates associated with yamhamelachite is the presence of two generations of barringerite, the earlier of which has higher Cr and V content. In the general crystallisation sequence, yamhamelachite appears after phosphides (+pyrrhotite, daubréelite) and then spinels of the chromite-magnetite series crystallise, along with ferromerrillite and ferroalluaudite. The source of chromium for yamhamelachite was mainly V-Cr-bearing pyrrhotite and V-bearing daubréelite. The low Fe³⁺ content in yamamelachite, likely related to its late-stage alteration, indicates that it crystallised from phosphate melt under reducing conditions at ~1000°С.