Granite varies in grain size too
Vive Cabeceiras · Complexo geológico de Cabeceiras de Basto · estudo regional

A seemingly uniform rock can reveal differences up close.

In A. Almeida’s study, granite from the Cabeceiras de Basto complex does not have a single grain size. The classification uses three average ranges: 0.5–1 millimetre for fine grain, 2–4 millimetres for medium grain and 5–7 millimetres for coarse grain. In the last group, the author also mentions rare larger crystals measuring 8–10 millimetres.

This distinguishes two observations: the usual grain size and the presence of a few crystals that stand out. The description does not turn every visible point in a photograph into a measurement. Comparing sizes in an image requires a scale; magnification on a screen can make small grains look large.

The study identifies three genetically independent series despite their similar chemical-composition ranges. Appearance is a starting point for investigation, not the entire explanation of origin. In a wall or façade, grains spark curiosity, but do not alone prove where the stone came from.

Sources and context
A. Almeida (1998) — Metallurgical specialisation of the peraluminous granites of two micas of the Cabeceiras de Basto complex, IGM 84(1), B-79–B-82; p. 325 of the PDF
https://eu-central-1.linodeobjects.com/socgeol-files/production/documents/168/original.pdf?1651938546=#page=325
Accessed: 2026-11-07

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