Igneous Petrology Series: Lesson 10 - Ternary Solid Solution Phase Diagrams

[@PreetiSingh-ct8xs]

Very well taught sir 👍

[@OtocerasWilliamsonia]

You made it easy and simpler. Thank you

[@malviyaaakash99]

Confused how to draw that blue line??

[@WillDSmith95]

Those 'black lines' in the lower half of the diagram are guidelines to mark the occurrence of equilibrated plagioclase at 90, 80, 70 mol.% anorthite etc. Since this is a continuum, where we initially intersect the cotectic line with our initial 'yellow line', we use those 'black lines' as a guide to see the composition of equilibrated plagioclase. For example, if our initial line intersects the cotectic at the same part the An 80 mol.% black line intersects - out first plagioclase will be 80 mol% An - it's fairly confusing with the lines, but hope this helps.

[@malviyaaakash99]

Very helpful. Thankyou

[@alireza8395]

in case for anyone else who might be confused, you draw a parallel line from the cotectic dipping towards Anorthite. Just like the fully shaded black line.