While it's considered extinct and hasn't erupted in a very long time, its formation is that of a stratovolcano. It was formed by layers of lava, ash, and rock that built up over time.

However, it's important to note that Aconcagua is also known as the highest mountain outside of the Himalayas. This is because its height and prominence make it a significant peak, even though it's not currently an active volcano.