At 10:47 AM 14/06/2002 +0200, Marcello Franceschelli wrote:
>Dear all,
> The calc-silicate rocks from the Hercynian chain of Sardinia (Italy)
> consist of wollastonite, calcite, diopside, grossular (quartz ,
> plagioclase) and pectolite. Can anyone suggest me the pectolite forming
> reaction and the P-T stability conditions?
Pectolite composition Ca2NaHSi3O9 is peralkaline; hence the
pectolite-forming reaction probably involves metasomatic addition of the
component Na2O.
Depending on your mineral assemblages, you may be able to estimate the
P-T conditions of pectolite formation from the equilibrium
grossular + quartz = 2 wollastonite + anorthite
and X(CO2) at the same P,T from
calcite + quartz = wollastonite +CO2 ,
as described by Skippen and Carmichael p.115-122 in Greenwood HJ editor
1977 Short Course in Application of Thermodynamics to Petrology and Ore
Deposits. Nowadays such P-T-X(CO2) calculations are made easy by the
PTAX/TWQ software package developed at Univ British Columbia.
Ciao, Dugald
Dugald M Carmichael Phone/V-mail: 613-533-6182
Dept of Geological Sciences and Geological Engineering
Queen's University FAX: 613-533-6592
Kingston ON K7L3N6 E-mail: [log in to unmask]
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