S-type asteroid

Approximately 17% of asteroids are of this type, making it the second-most common after the carbonaceous C-type.

S-type asteroids, with an astronomical albedo of typically 0.20,[1] are moderately bright and consist mainly of iron- and magnesium-silicates.

These largest S-types are visible in 10x50 binoculars at most oppositions; the brightest, 7 Iris, can occasionally become brighter than +7.0, which is a higher magnitude than any asteroid except the unusually reflective 4 Vesta.

The 1 μm absorption is indicative of the presence of silicates (stony minerals).

Due to their volatile-poor (rocky) composition, S-type asteroids have relatively high density.