"Katsuren travertine" is a paving stone produced from a porous marine limestone mined near Katsuren town orDOkinawa Island, Japan, that remains relatively cool under bright sunlight. As a pavement surface, it has promise as an effective material for mitigating the urban heat island effect, having a large heat storage capacity during the daytime and radiating modest amounts of heat at night. To quantitatively evaluate this material, we compared Katsuren travertine and ordinary concrete blocks by placing them in direct sunlight and monitored their surface temperature, conductive heat flux, radiation balance, and other parameters. In another trial, the concrete was covered with high-albedo paint closely fitting the optical properties of Katsuren travertine. In both trials, the travertine had a superior thermal performance as compared with concrete. We conclude that the high reflectance and thermal properties of Katsuren travertine make it a promising potential alternative to concrete to mitigate urban heat island effects. (C) 2014 Elsevier B.V. All rights reserved.