Evolution of surface properties of ornamental granitoids exposed to high temperatures

• Heated granitoids varied their properties of surface, colour and roughness.
• Grain size and mica content influence roughness variation.
• Colour changes are conditioned by mineralogy.
• Granitoids with clays from alteration did not experiment catastrophic failure.
• Surface properties are good indicators of thermal decay in granitoids.

Granite submitted to high temperatures may lead to the loss of aesthetic values even before structural damage is caused. Thirteen granitoids were exposed to target temperatures, 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. Damage characterisation, including roughness, colour and oxidation of chromogen elements by means of X-ray photoelectron spectroscopy (XPS) was assessed. Altered granitoids are more resistant to structural failure but redden rapidly. Black mica-rich granitoids turn into yellow with a maximum at 800 °C. Alkali feldspar-rich granitoids redden progressively due to iron oxidation. Roughness varies progressively in mica-rich granitoids, while in mica-poor granitoids, an increase in roughness precedes catastrophic failure.