Mineral
Aerenita
(Ca,Na)₆(Fe³⁺,Fe²⁺,Mg,Al)₄(Al,Mg)₆Si₁₂O₃₆(OH)₁₂(CO₃)·12H₂O · Silicatos (Inosilicatos)
Chemically it is a chlorine-hydroxy-borosilicate of calcium and aluminium that represents a major success for Spanish science. Although discovered in 1876, its exceedingly complex crystal structure remained an enigma for more than a century, prompting some to doubt it was even a real mineral. The mystery was resolved in 2004, when a Barcelona team led by Jordi Rius deciphered it and confirmed its validity with the IMA. It is also a historic pigment: the "Blue of the Pyrenees" used by Romanesque masters to paint the Virgin's mantles and the Pantocrator of Sant Climent de Taüll, achieving that characteristic blue without resorting to the costly lapis lazuli imported from Afghanistan.
Etymology
From the Greek "aerinos" (ἀέρινος), meaning "airy" or "colour of the sky", in reference to its blue colour.