The lake-dwellers used a variety of material; indeed, they seem to have been quite expert practical mineralogists. Characteristic is their use of certain rocks which combined great toughness and hardness, and were thus superior to flint; so chloromelanite, saussurite, nephrite, and jadeite. These minerals are rare, and the implements made of them were small chisel-like blades, rarely exceeding an inch in length. They were usually mounted in a socket of horn fastened into a wooden handle. We shall see that the source of these minerals is still anything but clear. The axe of the kitchen-midden[99] is hardly more than a disk struck off from a flint nucleus, with two sides broken off and the top of the triangular remnant removed. The axe of later Neolithic time was at first nearly of the shape of a flattened almond, but gradually changed and took more of the form of a chisel. The stages in this process of change are of value in determining the chronology of the period, and will be discussed in the next chapter. These axes were rudely shaped by flaking and then ground and polished on large flat stones, which still show the grooves left by the implement as it was rubbed back and forth. The different steps in shaping and finishing such axes are well shown by Hoernes in specimens selected from the rich collections made at Butmir, Bosnia. [Illustration: AXES FROM LAKE-DWELLINGS SHOWING ATTACHMENT TO HANDLES] The lake-dwellers followed a different and improved method. They selected from the bed of a stream a smooth pebble of somewhat flattened and elongated egg shape. With a flint flake or saw[100] and sand they cut a groove in the edge, and split the stone by a sharp blow, somewhat as a peanut or almond falls apart. The rounded surface of each half was nearly of the desired form, and only the flat surface required much shaping. A skilful workman now can finish an axe of this kind in half a day.[101]