The Dolomites are not primarily volcanic mountains; they are essentially fossilized ancient coral reefs and carbonate platforms. Roughly 250 million years ago, the area was a shallow tropical sea. Over millions of years, the remains of marine organisms built up massive layers of limestone and dolomite rock. However, there is a significant volcanic component to their history. Approximately 230 million years ago, massive volcanic eruptions occurred in the region, which covered the existing coral reefs with lava and ash. This volcanic activity is why you sometimes see dark, jagged volcanic rock interspersed with the pale, towering limestone peaks. The unique "Dolomite" rock itself was formed when magnesium-rich fluids (possibly influenced by the volcanic heat) altered the limestone. So, while the spectacular "cathedrals" of rock you see today are sedimentary in origin, the volcanic events played a crucial role in their geological "recipe" and the varied colors of the landscape.