QFL Diagram Plotter for Sandstone Provenance
Plot framework grain point counts on the Q–F–L triangle with the Dickinson provenance fields, and read sandstone source terrane straight off the diagram.
What a QFL diagram shows
A QFL diagram plots the three framework grain populations of a sandstone: Q, quartz (monocrystalline plus polycrystalline); F, feldspar (plagioclase plus alkali feldspar); and L, unstable lithic fragments. Only framework grains are counted — matrix, cement and accessory minerals are excluded and the three totals are then normalised to 100%.
Its value is that the mix of grains is inherited from the source terrane and modified by transport. Quartz survives almost anything; feldspar and lithics do not. So a quartz-rich sandstone means either a quartz-rich source, a long transport history, intense weathering, or recycling — and the position on the triangle, read alongside the geology, tells you which.
Data
Paste straight from Excel or Google Sheets — include the header row and the columns are matched by name, in any order.
| # | Q (quartz)% | F (feldspar)% | L (lithics)% | Sample(opt) | |
|---|---|---|---|---|---|
| 1 | |||||
| 2 | |||||
| 3 | |||||
| 4 |
0 rows of data
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Reading the provenance fields
The fields come from Dickinson and Suczek (1979) and Dickinson et al. (1983), and group into three broad terranes. Continental block sources (craton interior, transitional continental, basement uplift) sit along the Q–F edge: quartz- and feldspar-rich, lithic-poor. Magmatic arc sources sit along the F–L edge, becoming more quartz-rich as the arc is dissected and its plutonic roots are exposed. Recycled orogen sources sit along the Q–L edge — quartz plus sedimentary and metasedimentary lithics, with feldspar largely absent.
Two cautions worth carrying into any interpretation. Point counts should use the Gazzi–Dickinson method, in which a sand-sized crystal inside a lithic fragment is counted as that mineral, because otherwise the result depends on grain size rather than provenance. And the fields are empirical envelopes from modern sands, not hard boundaries: a point near a boundary is not a determination.
Common questions
- QFL or QmFLt?
- QFL separates stable from unstable grains and is the standard first look. QmFLt (monocrystalline quartz against total lithics, with polycrystalline quartz moved into L) discriminates recycled orogen sub-fields much better, so use it when that is the question.
- How many grains should I count?
- Three to four hundred framework grains per thin section is the widely used convention; below about 300 the counting error starts to rival the differences between fields.