QUARRIED MATERIAL
Much cabochon rough is extracted from its host rock by the use of considerable physical force, perhaps even explosives. Sometimes the quarried blocks are so large that they cannot be easily transported and must be further broken down into manageable pieces by means of sledge hammers. If the material is valuable throughout, it may pay the operator of the mine to saw the larger masses into smaller blocks at the mine even if considerable difficulty is involved in doing so. In primitive coun¬tries, or in extremely remote areas, the use of power equipment may not be feasible and it then becomes necessary to break up the blocks as best one can. This necessarily involves considerable loss because the mere act of hammering means applying destructive stress to the stone and creating cracks which radiate in all directions from the points of impact. There is an art to breaking down large masses of rock so that the least damage is done except where it is wanted, but much good gem material has been destroyed by poor hammering techniques and later sold to the unwary who believe it to be sound.

Rough blocks can be a gamble unless they are carefully inspected for signs of hammering damage. One should look for the telltale whitish, crumbly places on the surfaces of blocks which are the remnants of ham¬mer blows. Beneath each one is likely to be a network of cracks radiating deeply into otherwise sound material. Such damage is inclined to be particularly severe in brittle materials such as jasper, chert, petrified wood, rose quartz, and obsidian; or in cleavable or splittable materials such as feldspars, some types of nephrite jade, sodalite, and serpentine. On the other hand, granular materials such as rhodonite and jadeite tend to absorb the shock of misdirected blows a short distance below the surface and the damage is usually confined to smaller areas.

Cracked rough is not necessarily undesirable if meant for cutting into small articles, but it can be troublesome during slab sawing because of the tendency for sections to fall out prematurely and damage the blade. Cracked rough is definitely undesirable when large flawless masses are required for such items as book ends, spheres, and carvings.