Granite also changes grain

In the study by A. Almeida, the granite complex of Cabeceiras de Basto does not have a single grain size. The classification uses three average intervals: 0,5–1 millimeter for fine grain, 2–4 millimeters for medium and 5–7 millimeters for coarse grain. In the last group, the author also mentions rare larger crystals, with 8–10 millimeters.

This allows distinguishing two observations: the usual size of the grains and the presence of some crystals that stand out. The description does not transform each visible point of a photograph into a measurement. To compare sizes in an image, a scale is required; a magnification on the screen may make small grains look large.

The study refers to three genetically independent series, although they have similar chemical composition ranges. Appearance is an entrance to research, not all explanation of origin. On a wall or a façade, the grains arouse curiosity, but do not prove for themselves where the stone came from.