Evaluation of dimension stone in gneissic rocks - a case history from southern Finland

A dimension stone prospect in southern central Finland was assessed by a de tailed mapping, gee-radar survey, and core drilling. The prospect is a vein ed and bedded garnet-cordierite gneiss, consisting of a dark; schistose med ium-grained palaeosome and a light coarse-grained granitic leucosome. Both components are found mainly as thin units, but the leucosome can occur as i ndividual veins several metres thick, which leads to disturbing variations in the appearance of the stone. The soundness of the stone is defined by th e amount of tight, but open cracks in the palaeosome and weakness zones in the weathered leucosome. As a whole, the soundness is diminished down to 10 m below the outcrop surface. Furthermore, a subhorizontal body of younger granite is identified at approx. 8-20 m depth. Consequently, the prospect i s not feasible for production of dimension stone. The core drilling was decisive in the final evaluation of the prospect beca use the true density of the cracks and the subsurface granite were identifi ed by the method. Only with the use of core drilling could the proper inter pretation of the characteristics of the prospect be made, demonstrating the importance of three-dimensional investigation of a dimension stone prospec t. (C) 2000 Elsevier Science B.V. All rights reserved.