Feldspathoids are a group of minerals that are similar to feldspars but have a lower silica content. They are typically found in volcanic rocks and are important for understanding the composition of the Earth's crust. Common types of feldspathoids include nepheline and sodalite, which can form in specific geological environments. These minerals are often used in ceramics and glassmaking due to their ability to lower melting temperatures. Feldspathoids can also provide insights into the conditions under which certain rocks formed, making them valuable for geologists studying igneous processes and the evolution of the Earth's crust.