What is the second most abundant element in the earth's crust?

Silicon is indeed the second most abundant element in the Earth's crust, following oxygen, which makes up a significant portion of the crust. Silicon constitutes about 27.7% of the Earth's crust and is predominantly found in the form of silicate minerals, which are essential components of many rocks. This high abundance is largely due to silicon's ability to easily combine with oxygen to form silicon dioxide (SiO2), or quartz, and various silicate minerals that dominate the Earth's crust.

The other elements, while also important, do not match silicon's abundance. Aluminum is the third most abundant element but is significantly lower than silicon in terms of percentage. Iron, while abundant, primarily exists in the Earth's core and its deeper layers rather than the crust itself. Calcium, despite being an important element for biological systems and present in sedimentary rocks like limestone, is less prevalent than silicon in the crust overall. Thus, through its widespread presence in multiple mineral forms, silicon earns its position as the second most abundant element in the Earth's crust.