Ermeloite, AlPO4⋅H2O a new phosphate mineral with kieserite-type structure from Galicia, Spain

Abstract

Ermeloite is a new aluminium phosphate mineral from Galicia, Spain, in the northwest of the Iberian Peninsula. It is the third formally recognised mineral discovered in Galicia since morenosite and cervantite in the 19th Century. The name and symbol (Erm) were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2021–017a) in recognition of the geographical location where it was found. The mineral occurs as a light blue to white fine aggregate over quartz and microcline associated with wardite. Crystals of ~0.04 mm are transparent and have a waxy lustre. The simplified empirical formula determined using electron microprobe analysis is Al1.02P0.95F0.06O3.88⋅1.06 H2O, which is near to the ideal formula Al(PO4)⋅H2O. The mineral is an alteration product within a phosphate pegmatite. Ermeloite is the second phosphate isostructural with the sulfates of the kieserite group. Single-crystal X-ray diffraction showed that ermeloite crystallises in the monoclinic C2/c space group with cell parameters a = 6.5371(4) Å, b = 7.5670(5) Å, c = 7.1146(5) Å, β = 115.335(2)°, V = 318.08(4) Å3 and Z = 4 at room temperature. Comparative analysis of the crystallographic data, with isostructural phosphates, revealed an interesting behaviour for these compounds.