Dear Tharange,

bound water = H20+,

moisture water H,O-,

LOI: see http://en.wikipedia.org/wiki/Loss_on_ignition

So LOI usually is all water, including bound water (crystal water) and moisture. The temparature to which the material is heated for LOI determines whether or not water from dehydroxylation (of e.g. mica's) is  taken into account. Dehydroxylation of micas takes place at some 500 degrees centrigrade.

Hope this helps.

Regards,

Jack Voncken

Delft University of Technology.

Thank Dr Jack

Actually LOI means "loss on ignition", therefore the sample has reached a temperature in which all volatiles are eliminated, this includes moisture water plus bound water in micas, amphiboles, epidote, etc. [in the form of (OH)-], and in some rocks even CO2 produced by decomposition of carbonates. If no carbonate is present, then LOI is H2O+ plus H2O-. LOI heating I understand that reaches some 700°C.  

Dear Sir, I want to make pseudosection diagrams. For that I want weight % of H2O. So how to calculate the weight % of H2O from XRF data, when LOI is given in the data.

In some cases it is important to consider that LOI values are not simply the result of volatile losses (water, carbonate, organic matter).  Some processes that occur during heating to high temperature also produce weight gains.  These may offset the weight losses from volatile elements or even cause a net weight gain during heating (negative LOI value).  A primary example is material that contains high FeO which is converted to Fe2O3 by oxidation.  Some iron-rich basaltic rocks which are low in volatile components will yield negative LOI values as a result of oxidation.

Just a correction LOI has nothing to do with the XRF analysis. LOI is obtained gravimetrically by heating the sample.

Another contributor to the LOI is SO2, which can be either primary in your rock or secondary, due to the oxidation of rock's sulfides in air.