Polonnaruwa Gal Vihara granite mineralogy: charnockitic gneiss durability and weathering resistance?
What mineral quartz-feldspar ratios and chemical composition make the charnockitic gneiss of Gal Vihara exceptionally resistant to tropical weathering?
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3 Answers from travellers
The four monumental Buddha sculptures of Gal Vihara in Polonnaruwa are carved from a continuous 50-meter outcrop of high-grade charnockitic gneiss belonging to the Highland Complex of Sri Lanka. Mineralogically, charnockite is a hypersthene-bearing granitic rock comprising interlocking crystals of quartz, plagioclase feldspar, microcline, and orthopyroxene. This anhydrous mineral assemblage lacks hydrous micas and clays, endowing the rock with exceptional mechanical hardness and resistance to chemical hydrolysis under high humidity and monsoon rainfall, allowing unreinforced stone statues to endure for eight centuries.
Dark mineral streaks visible across the Buddha statues are natural orthopyroxene crystal bands integrated into the gneiss formation.
A modern open steel-and-tile canopy installed by archaeologists shelters the fragile rock carvings from direct solar UV radiation and acid rain.
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