Answer to Question 1
Answer: Both are silicate minerals, dominated by the elements silicon and oxygen, arranged in the silicon-oxygen tetrahedron. Light silicates tend to have larger amounts of sharing between their silicon-oxygen tetrahedral, while dark silicates tend to have less sharing (more oxygen atoms for every atom of silicon. Light silicates tend to include sodium and potassium in their crystal structure, while dark silicates tend to include magnesium, iron, or calcium.
Answer to Question 2
B