Usage
QAPF diagrams are mostly used to classify plutonic rocks (phaneritic rocks) (Figure 1), but are also used to classify volcanic rocks (Figure 2) if modal mineralogical compositions have been determined. QAPF diagrams are not used to classify pyroclastic rocks or volcanic rocks if modal mineralogical composition is not determined, instead the TAS classification (Total-Alkali-Silica) is used. TAS is also used if volcanic rock contains volcanic glass (such as obsidian). QAPF diagrams are also not used if mafic minerals make up more than 90% of the rock composition (for example: peridotites and pyroxenites).
An exact name can be given only if the mineralogical composition is known, which cannot be determined in the field. Therefore, provisional or field classifications (Figures 3 and 4) are used, which are simplified versions of Figures 1 and 2.
- QAPF diagram gallery
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Figure 1. This classification is used if rock sample has phaneritic texture (plutonic rocks).
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Figure 2. This classification is used if rock sample has fine-grained texture (volcanic rocks) but modal mineralogical composition can be determined.
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Figure 3. This is provisional classification for phaneritic igneous rocks (field classification).
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Figure 4. This is provisional classification for fine-grained igneous rocks (field classification).
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