Ewingite
A magnesium-calcium uranyl carbonate with 138 water molecules — the most chemically complex mineral known when discovered in the Plavno mine.
Intro adapted from Wikipedia (CC BY-SA).
Ewingite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Mg₈Ca₈(UO₂)₂₄(CO₃)₃₀O₄(OH)₁₂(H₂O)₁₃₈.
It crystallizes in the tetragonal crystal system (space group I4_1/acd).
Key properties: Mohs hardness 2; specific gravity 2.525; Pale yellow streak; Vitreous luster; optically uniaxial.
IMA symbol Ewg, IMA status: approved, named in 2016.
A secondary mineral formed by postmining oxidation of primary uraninite in a wet environment on a damp wall in an abandoned underground mine.
It is found associated with Liebigite, metazellerite, gypsum, uraninite.
The mineral was named to honor Rodney C. Ewing (b. 1946) mineralogist and material scientist focused on the properties of nuclear materials at Stanford University, California, USA.