The granite intrusion in the Setul Formation limestone has caused molten magma (1000°C) to penetrate the cracks and bedding of the rocks. Pulau Tuba Sill Geosite is a phenomenon of granite magma infiltration between layers of sedimentary rock found in limestone outcrops near the old Tuba jetty (Tuba Bay). Here, there are two layers of granite sills, 1.5 m and 1 m thick. This event occurred during the implacement of Mount Raya Granite (Triassic Period, around 220 million years) pushing up sedimentary rocks from the ocean and exposing Langkawi’s ancient land. Sill formation is a rare phenomenon in geological processes that occur at the boundary between igneous intrusion and surrounding sedimentary rocks.

The interaction between molten magma and the surrounding rock can result in the formation of new minerals. Scientists often look for such an important evidence of geological heritage. Unfortunately, the locals are not yet aware of this important site. The development of geosite for education can increase public awareness and appreciation of local heritage.

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