• journal_title：The Canadian Mineralogist
• Contributor：Marie-Lola Pascal ; Michel Fonteilles ; Omar Boudouma ; Claudia Principe
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.2.459
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：2
• firstpage：459
• section：Articles

Qandilite (Mg₂TiO₄) and magnesioferrite occur in forsterite – spinel – calcite skarn ejecta from Mt. Vesuvius, Italy, with an exceptionally large compositional range that outlines the miscibility gap in the system spinel – qandilite – magnesioferrite (with a small amount of Fe²⁺), at present solely determined on the spinel–qandilite binary at T > 1000°C. The analyzed spinel– qandilite and spinel–magnesioferrite pairs are consistent with the solvus and tie-lines (except for a temperature offset) derived from the thermochemical model of spinel solid-solutions. Temperatures of formation in the range 650–700°C are inferred from the petrological study of the skarn-forming processes involved, which typically include two types of metasomatic reactions, i.e., formation of spinel – forsterite – calcite endoskarns by desilication of aluminosilicate bodies at the contact of dolostone wallrocks, and reaction of such pre-existing endoskarns with new influxes of magma ± fluid. Calculated phase-relations among qandilite, perovskite and geikielite show that qandilite with moderate magnesioferrite contents is the high-temperature Ti mineral stable in magnesian and extremely silica-deficient surroundings under oxidized conditions.