Sri Lanka is part of a Precambrian craton, some two billion years old metamorphic rocks. Such rocks were originally sedimentary rocks but were transformed by a long series of crust movements, subsidence, high pressure and temperature inside the earth. This craton is a part of the supercontinent Gondwanaland and was connected with the craton of the Indian subcontinent until it collided with the Asian plate and formed the Himalaya some 45 Million years ago. After this collision, the small piece which is the base of Sri Lanka was separating from the Indian plate. This separation caused earthquakes and volcanism which created some volcanic rocks on the island.
The geologic history of the island results in a huge amount of metamorphic rocks, but also a small amount of volcanic and sedimentary rocks. The metamorphic rocks are rich in mineral deposits, including iron ore, zinc, manganese, molybdenum, nickel, cobalt, arsene, wolfram, tellurium, and gold. There are numerous precious gems found on the island too, rubies, sapphires, topaz, and spinel. Unfortunately, the history of the country did not result in the development of show mines so far, although it is a popular tourist destination.
There are only very few natural caves of limestone in isolated spots. Most common are erosional caves in all kinds of rocks, created by erosional forces of the tropic climate. However, they are always of limited depth, more or less overhanging cliff faces and abris. Nevertheless, they were used over the centuries as hermit's homes and to build temples or Buddha statues inside. There are several cave temples in the country.