Another old model brought back to life. This is the Click on the image below to see the model in action.  This is the ternary system quartz – nepheline – kalsilite, also called petrogeny’s residua system, which is used to describe the composition of many cooled residual magmas and the genesis of very under saturated alkaline rocks.

More on this classification, used for cooled residual magmas, on Alessandro Da Mommio’s website, for example his page on Tracheite.