This is a picture of the Main Belt. The Main Belt has billions of Asteroids. Most asteroids are mainly rocky bodies that orbit Sun between Mars and Jupiter. The Main Belt that is centered around 2.7 times the Earth's distance from the Sol.

"As dark as soot, carbonaceous asteroid 253 Mathilde is rich in carbon compounds

and other dark substances common in carbon in the outer region of   the Main Asteroid Belt.

Mathilde is like a loose rubber pile with density of water."

            It has been estimated that the total mass of the Main Asteroid Belt may total less than about 1/1000th of the mass of the mass of the Earth. The Main Asteroid Belt would measure about less than 1,300 to 1,500km (810 to 930miles)across. The Main Asteroid Belt is only a small remnant of the material that resided in the region between Mars and Jupiter.

    Based on the composition of meteorites found on the Earth , most asteroids may be composed of three materials: mostly (92.8 percent) silicates ( stone) metals (5.7 percent) iron and nickel; and the rest as a mix of those materials and carbon- rich substances. Circum-Solar dust disk out of which the outer plants accreted about 4.5 billion years ago. Thus, the outer asteroids may more closely resemble the icy planetary bodies.