Final answer:
Asteroids are irregular in shape and consist of rocky or metallic materials. They have surfaces coated with gray rock and can be classified primarily as C-type or S-type, depending on their composition and reflectivity. Some asteroids show signs of early volcanic activity with basaltic surfaces.
Step-by-step explanation:
Asteroids are irregular in shape and rocky or metallic in composition. Their surfaces are covered with gray pulverized rock. Spectral studies reveal that darker asteroids, known as C-type asteroids ("C" for carbonaceous), are primitive bodies composed of silicates mixed with dark, organic carbon compounds.
These types of asteroids, which include some of the largest like Ceres and Pallas, have remained chemically unchanged since the beginning of the solar system. In contrast, the S-type asteroids are composed mainly of silicate minerals without the dark carbon compounds found in C-types, thus having higher reflectivity and different spectral signatures. Lastly, M-type asteroids exhibit signs of early heating and have basaltic surfaces similar to the volcanic plains found on the Moon and Mars.