Question on predominance diagram plot

[kangmingliang]

Dear Sir/Madam,

 

May I ask how to plot the predominance diagram (see the attached figure) for K-feldspar with Act2-GWB? I saw the predominance diagram of K-feldspar from literature, but I do not know how to plot it with GWB. Thank you very much for your guidance.

 

Looking forward to your timely response.

 

Best regards

 

Mingliang

[Brian Farrell]

Hi Mingliang,

 

There is actually a diagram very similar to this on the Diagrams page of our website. Find the Act2 section, choose Mineral Stability, then click the Act2 icon to open Act2 with the diagram already made on your computer (assuming you have GWB). Now you just need to edit the diagram.

 

Note that SiO2(aq) and H4SiO4(aq) are commonly used interchangeably to represent uncharged dissolved silica in geochemistry. Just change the axes ranges to match the diagram, and you get the first image I've attached.

 

After this you'll want to suppress minerals that weren't considered in the original diagram. Using the GUI, go to Config - Suppress to do this. You'll want to suppress Pyrophyllite and Clinoptil-K, then a few more that come up in their place, until you get something that looks like image 2 below, which is very similar to your diagram. (Alternatively suppress all minerals, then unsuppress Gibbsite, Muscovite, Kaolinite, and K-feldspar, which is basically how a diagram would be made by hand)

 

You'll notice the stability fields for each mineral differ slightly between the original and GWB diagrams - this is likely because the logK values used by the original author differ from the default GWB database. If you can track down the original source, use the Alter logK function within GWB to quickly adjust your 25C equilibrium constants. Here I've adjusted Muscovite (K mica) and Kaolinite.

 

Hope this helps,

Brian Farrell

Aqueous Solutions LLC

Edited January 10, 2012 by Brian Farrell