What type of rock is Sigiriya rock made of?

Sigiriya rock is mostly made of syenite, which is a coarse-grained intrusive igneous rock that people often categorise as a kind of granite. This huge monolith is basically an erosional remnant, meaning it started out as the hardened magma plug from a volcano that is no longer active, and that volcano is now considered extinct.

It formed more than two billion years ago, during the Precambrian period. Back then, the molten magma pushed into older rock layers, and it cooled slowly, then solidified underground. Over millions of years, the outer volcanic cone got worn down by wind and rain, so in the end, the very hard syenite magma shaft was left exposed. The syenite makeup is heavy in orthoclase feldspar and quartz, and that mineral mix gives the rock serious structural durability. Because of that, a stable foundation was there for King Kashyapa to build his detailed palace and fortress complex at the summit in the 5th century CE.