THE COLOR OF SOME JORDANIAN BUILDING LIMESTONES IN THE DRY AND WET STATES

The color of twelve Jordanian building limestones assigned using the Munsell Rock Color Chart (MRCC), was found not accurate enough especially in the wet state. This is believed to be due the limited number of rock chips included in this chart. Hence the color, in the dry and wet states, was measured by a colorimeter using the L*a*b* color system. Color differences were expressed by ∆E and ∆C (chromaticity). In the dry state, the highest L* and E values were recorded in a creamy white coquinal limestone and the lowest in travertine. Chalk recorded the highest a*, b* and C values, whereas a gray-black limestone has the lowest b*, E and C values. In the wet state, the creamy white limestone has the highest L* and E values and the lowest a* value. Chalk has the highest a*, b* and C values. The gray-black limestone has the lowest b*, E and C values. Upon wetting L* and E decrease, while a*, b* and C increase. The highest ∆E occurs in the gray-black limestones, an intermediate change occurs in fine and coarsely crystalline limestones, followed by colored chalks. Other types of limestone have a low change in E. In the case of ∆C, the greatest change occurs in colored chalks, followed by the very fine-grained limestone, crystalline rocks and finally the fossiliferous limestones. Four broad color fields (cream-white, gray-black, yellowish, and reddish-pinkish) can be distinguished in the ∆E-∆C graph. The color in the wet state can be derived from that of the dry state using the graphs made in the present work.