Yamhamelachite, KCrP ₂ O ₇ , a new natural pyrophosphate from phosphide-bearing breccia of the Hatrurim Complex, Negev Desert, Israel

Abstract 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, KCrP 2 O 7 ( P 2 1 / c, a = 7.3574(3), b = 9.9336(4), c = 8.1540(4) Å, β = 106.712(5)°, V = 570.77(5) Å 3 and 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 0.89 Ca 0.01 □ 0.10 ) Σ1.00 Cr 3+ 0.50 V 3+ 0.33 Al 0.15 Fe 3+ 0.04 Ti 4+ 0.03 ) Σ1.05 P 1.98 O 7 . The density calculated from the empirical formula and structural data is 3.035 g·cm –3 . Cr 3+ in yamhamelachite is substituted by V 3+ , and in a few cases V is marginally more abundant than Cr, indicating the presence of a potentially new mineral with the formula KVP 2 O 7 . Yamhamelachite consists of layers of Cr 3+ -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 and 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 Fe 3+ content in yamhamelachite, probably related to its late-stage alteration, indicates that it crystallised from phosphate melt under reducing conditions at ∼1000°С.