Aquamarine is a blue or blue-green variety of the mineral beryl. It is typically formed in pegmatites, which are coarse-grained igneous rocks that form from slow cooling magma or lava.
During the formation of pegmatites, fluids rich in aluminum, beryllium, and other elements become trapped in the rock as it cools. These fluids help to concentrate and crystallize the mineral beryl, which can form large, well-formed crystals in the pegmatite. Aquamarine gets its color from the presence of iron ions in the crystal structure.
Aquamarine can also be found in mica schist and granite as well as in alluvial deposit, when weathering and erosion of the primary rock cause the beryl crystals to be transported and redeposited in a new location.
In summary, aquamarine is formed from the mineral beryl, which crystallizes from fluids trapped in pegmatite rocks, through the process of slow cooling of magma or lava. Other mineral can be found in mica schist and granite, and also as an alluvial deposit.