Dark silicates have a specific gravity of 3.2 to 3.6 and are composed primarily of silica tetrahedral and select one: a. aluminum and magnesium b. potassium and iron c. potassium and calcium d. aluminum and sodium e. iron and magnesium

The correct answer is E. Iron and magnesium

Explanation:

Silicates are the most abundant type of minerals in Earth, these are the result of the combination of silicon and oxygen along with other materials. Additionally, not all silicates are identical but differ in composition and physical/chemical features. Indeed, silicates are often classified as dark or dark silicates. In the case of dark silicates, these include different types of silicates such as olivine and biotite that are dark because they contain silica tetrahedral but also iron and magnesium. Thus, dark silicates are primarily composed of silica tetrahedral and iron and magnesium, which is also why they are known as ferromagnesian silicates.