Final answer:
Igneous rocks are primarily classified based on their composition and texture, not color. Hence, the correct answer to the question is D composition and texture is the correct answer.
Step-by-step explanation:
Igneous rocks are classified based on composition and texture. Composition refers to the chemical makeup and the minerals present in the rock, while texture refers to the size and arrangement of these minerals. Color does play a role as certain minerals have characteristic colors, but it is not a primary classification factor.
For instance, a rock consisting mainly of green olivine minerals would be classified as ultramafic due to composition, not just color. Moreover, the rate of cooling affects the texture; slow cooling results in larger mineral grains as seen in intrusive or plutonic rocks, while fast cooling usually produces smaller grains typical of extrusive or volcanic rocks.
With these considerations, the correct classification properties of igneous rocks are their composition and texture. Therefore the correct answer to the student's question is D. composition and texture. Please note this when mentioning the correct option in the final answer with the number 500 involved.