This Siderastrea does not form large colonies, but is usually encrusting and may form free living mobile balls. Corallite centers are sunken, inner septal lobes are steep and the individual, thick septa can be seen easily underwater.

It is very pale, light grey or tan, with dark, sunken centres.

It is very similar to S. stellata, but the latter has twice as many septa (like S. siderea in this respect) and appears to have deeper calices.