Two bores were drilled in the weathered zone of a Precambrian dolomite at Fowler's Gap, 100 km N of Broken Hill, New South Wales. Five weathering units have been distinguished: fresh dolomite; weathered dolomite, type B; weathered dolomite, type A; ferricrete; and surface hardened dolomite. Physical and mechanical properties show variation throughout the weathering profile, and are related to the fabric of the rock, especially to the fracturing intensity, which is a function of degree of weathering; and to secondary surface silicification. A tentative engineering classification of the weathered dolomite is proposed.