Essaïd Bilal
Beryllium-bearing minerals such as beryl, phenacite, and helvite are identified within quartz-muscovite and siderophyllite veins, with an emphasis on phenacite and helvite (Fe,Zn,Mn) 8Be6(SiO4)6S2 in albitites. This study focuses on helvites from the Sucuri deposits in Goiás, Brazil, and northern Costabonne skarn (France) and quartz-wolframite veins from Dajishan (China). Through the analysis of paragenetic and geochemical data from these occurrences, a new structural formula is proposed: (Mn,Zn,Fe)8-xNax Be6 Si6 O24 S2-xClx, which is akin to that of haüyne. Various substitutions, including Zn-Fe-Mn and Cl-S, are acknowledged, and it is suggested that lithium may substitute for beryllium while sodium compensates for the charge deficit. Crystal chemical constraints also influence the incorporation of rare earth elements, particularly heavy REE in an alkaline environment. Distinct stability conditions for danalite, genthelvite, and helvite underscore their different compositional stability across varying fS2 and fO2 levels. The compositional variation of beryllium minerals, including the role of aluminum activity, is associated with the mineral's stability in relation to the geological conditions, indicating a complex interplay of geological processes that enhance or inhibit mineral formation.
@article{941a2c6b-15ca-48f0-a837-d698fa7242d5,
title={Geochimie et Conditions De Cristallisati},
author={Essaïd Bilal},
year={2026},
language={en}
}TY - JOUR TI - Geochimie et Conditions De Cristallisati AU - Essaïd Bilal PY - 2026 LA - en ER -
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