What low-density substance mainly makes up earth's crust?

The Earth's crust is primarily composed of low-density silicate minerals, with a significant portion made up of feldspar, quartz, mica, and amphibole. These minerals are rich in silicon and oxygen, forming the foundation of continental and oceanic crust. The average composition of the crust is about 45% silicate minerals, which contribute to its relatively low density compared to the underlying mantle.