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Formula: KCrP2O7
Valence: KCr3+P2O7
Anhydrous phosphate of potassium and chromium
Crystal system: Monoclinic
Specific gravity: 3.035 calculated for the empirical formula
Hardness: 4
Streak:
Colour: Green
Luminescence:
Solubility:
Common impurities:
Environments
Yamhamelachite is a new mineral, approved in 2023.
Localities
The type locality is the Arad – Dead Sea road, Wadi Zohar, Hatrurim Basin, Tamar Regional Council, Beersheba
Subdistrict, Southern District, Israel. High-temperature pyrometamorphic rocks of the Hatrurim Complex and their
alteration products are distributed widely along the Dead Sea rift in the territories of Israel, Palestine and Jordan.
The most typical rocks are spurrite
marble,
larnite
pseudoconglomerate and
gehlenite
hornfels. The highest temperature rocks of the Complex are
paralavas of various types, most of which comprise oxidised mineral
associations. The rarest type encompasses diopside-bearing and
gehlenite-bearing reduced
paralavas, which are associated with the presence of phosphides.
Yamhamelachite was discovered in phosphide-bearing breccia found
in 2019 in the Hatrurim Basin on the artificial outcrop formed as a result of the construction of the Arad-Dead Sea road.
This unique and highly inhomogeneous breccia has cement composed of
gehlenite, flamite
(±rankinite,
pseudowollastonite)
paralava.
Yamhamelachite is a rare mineral in the breccia and forms thin
zones of 2 to 3 µm on zonal aggregates of phosphides with the following zonation:
barringerite → schreibersite
→ eutectic: schreibersite
+ native iron. Phosphides are concentrated at the boundary of the
paralava and thermally altered sedimentary xenoliths. Inclusions of
Cr–V-bearing pyrrhotite are often noted at the rim of these aggregates. The
occurrence of late-generation barringerite replacing
schreibersite, and its association with minerals of the
merrillite subgroup and
fluorapatite is a characteristic feature of phosphide aggregates with
yamhamelachite. In one case, a zone of yamhamelachite up to 30 µm thick was found in the
hematite aggregate formed after
pyrrhotite. Next to this yamhamelachite is a zoned aggregate:
barringerite I → eutectic:
schreibersite + barringerite
→ barringerite II → yamhamelachite →
chromite + magnetite →
ferromerrillite. The
eutectic zone contains
daubréelite inclusions, and partially oxidised
pyrrhotite inclusions were noted in
barringerite II. Pyrrhotite was
widespread in the rock, which often had lamellae of Cr- and V- enriched
pyrrhotite and/or daubréelite.
In samples containing yamhamelachite, pyrrhotite was almost completely
replaced by hematite, forming characteristic framework
pseudomorphs reminiscent of the lamellar structure of
pyrrhotite.
Yamhamelachite forms dark green granular aggregates in which the grain size does not exceed 25 to 30 mm. The
mineral is transparent with a glassy lustre. Yamhamelachite is a brittle mineral, with a conchoidal fracture
indicating a lack of cleavage. Yamhamelachite grains are usually very small (∼10μm) and intergrown with
iron oxides
(MM 89.5.664-674).
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