Extraction by blasting techniques is rarely used in most sedimentary dimension stone quarries and only sparingly in the harder igneous and metamorphic slate quarries.

The strength and durability of stone is affected by many natural factors such as jointing, cleavage, bedding etc. and quarrying companies have generally learned, by experience, to take full advantage of such factors in the production process. A knowledge of the size and orientation of any major joint sets, for example, particularly in igneous rocks which have no natural bedding planes, is particularly relevant. Natural joints are produced by stress release as the rock is exposed at the earth surface, and tend to have discrete and predictable regional trends. They cause the rock to split naturally into relatively regularly sized blocks. Such joint patterns can have significant effects on the way in which a quarry operator develops the quarry face. In contrast, while jointing is also often a common feature of sedimentary rocks, their characteristically bedded nature also exerts control on the size of block which can be produced. The techniques used to initially extract stone blocks have tended to exploit such natural lines of weakness.

Penrhyn slate quarry Gwynedd

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