Use this geological calculation for a transparent first-pass interpretation of measured rock, soil, fluid, well, stratigraphic, isotopic, geophysical, or seismic data under an explicitly selected model.

Q

Quartz modal volume percent.

A

Alkali feldspar modal volume percent.

P

Plagioclase modal volume percent.

F

Feldspathoid modal volume percent.

Normalize modal quartz, alkali feldspar, plagioclase and feldspathoid contents to QAPF coordinates and pick the plotting triangle. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Q%

Normalized quartz coordinate (percent of Q+A+P+F).

A+P%

Normalized combined feldspar coordinate.

F%

Normalized feldspathoid coordinate.

Triangle

Triangle selected by the IUGS double-triangle rule.

• Classification diagrams and geochemical ratios require appropriate normalization, oxidation-state treatment, volatile basis, analytical quality, alteration screening, mineral or whole-rock context, and a composition within the method's calibration domain.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Compare independent measurements and models, retain units and analytical metadata, propagate uncertainty, and validate interpretations against logs, cores, maps, laboratory data, or field observations.

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