Stability Relations "UlrT-3i-'3:Quartz in the System

Isobaric log 16,-Z phase relations for the reaction andradite * quartz: hedenbergite * wollasto-nite I | /2 Or in the Ca-Fe-Si-O-H system were experimentally determined at 500 and 2000 bars Pn ia and temperatures from 400o to 900'C using conventional techniques with solid phase oxygen buffers to control lo,. With fe, values defined by the Ni-NiO buffer, the assemblage andradite * quartz + fluid is stable up to 600oC at 500 bars and 680"C at 2000 bars Pnuia. fn the lower 16. range, the assemblage hedenbergite- | wollastonite * fluid is stable above about 350'C. The high-tempera-ture and high-le, assemblage of equivalent composition is wollastonite + magnetite (or hematite) + quaftz * fluid. The low-temperature assemblage is ilvaite * wollastonite (or xonotlite) * fluid. Combined with the previously determined equilibria for wollastonite, andradite, hedenbergite, and ilvaite, chemographic analyses interrelating the phases andradite (Ad), hedenbergite (Hd), wollastonite (Wo), ilvaite (Iv), magnetite (Mt), calcite (Cc), and quartz (Qz) in saturated SiOz conditions in the system Ca-Fe-Si-C-O-H permits the locations of invariant points on alogto,-T diagram. It also delineates isobaric T-le, conditions of formation for the assemblages Ad+Iv+Qz, Hd*Iv*Qz