SUMMARY Commonly used variation diagrams do not convincingly distinguish strongly alkaline, alkaline and calc-alkaline rocks over the full range of silica contents, especially for more acid varieties. In particular, the Rittmann Suite Index, a, becomes invalid once SiO2 exceeds about 70%.
No takes yet. Share an insight, caveat, or question.
Jack Wright (1969) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: