Complex sentence: Apxoximately 17% of all known asteroids are of an S-type, a relatively bright (albedo 0.10 to 0.22) asteroid, consisting of metallic nickel-iron mixed with iron-and magnesium-silicates.
Split into simpler sentences: Apxoximately 17% of all known asteroids are of an S-type. They are a relatively bright (albedo 0.10 to 0.22) asteroid, consisting of metallic nickel-iron mixed with iron-and magnesium-silicates.