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The Indigenous Stones of Great Britain

 

Limestone

 

Stone is a material that man has used in building for several thousand years and it still lends itself to modern usage and design, and limestone in its various geological forms is probably the type of natural stone most widely used for this purpose. It occurs naturally in many parts of the UK with the limestones of the Jurassic period being those of most importance in this field. They run broadly in a belt from Dorset and Somerset in the south west, through the Cotswolds and Oxfordshire, on into Northamptonshire and Lincolnshire, to just north of the Humber.

Limestone is a sedimentary rock. Many of the commonly used varieties were formed by the accretion of the hard remains of former organisms such as corals and shells. These materials principally comprise calcium carbonate (calcite), as does the cement. Calcite is a relatively soft mineral and careful selection will be needed when you choose this for use as flooring. Variations in the types and quantities of shell and other remains and the nature of the cement provide a huge range in the types of limestone available.

The limestones of these areas were used for building in Roman times and, in later centuries and to-date, have been the traditional building material of their localities. Many buildings throughout these counties bear witness to this. In addition, some limestones are extensively used outside their areas of origins as is evidenced by the many fine buildings to be seen throughout the British Isles, particularly in major cities and towns. Cathedrals, churches and numerous public and private buildings provide outstanding examples of the durability and beauty of these limestones and they show through the skill of the mason, how this stone is so eminently suitable for producing masonry of excellence in all aspects of plain and detailed work that may be required. Among the better known limestones of the Jurassic age are those of Purbeck, Clipsham, Ancaster, Ketton, Bath, Doulting and Weldon, whilst Portland stone is a characteristic feature of London architecture. From the earlier Carboniferous age come the limestones of Derbyshire and Cumbria such as Hopton Wood, Sheldon, Orton Scar and Salterwath.

Sandstone

The term sandstone is used to describe almost any stone of sedimentary origin with a granular texture. Some other types of stone that may fall under this classification include gritstones, siltstones, greywackes, conglomerates and marls. Aside from particle size variations, the dominant factor affecting sandstone performance is the grain cement that may be siliceous, calcareous, clay bearing or iron-rich.

Geologically it is a sedimentary type rock made up of various mineral particles mainly quartz, mica and felspar. All these minerals are bonded together with natural cements such as silicas, calcium carbonates, iron oxides and clays. The individual make up of each sandstone gives a wide range of colours. A pure silica sandstone is white with the colours arising from other minerals. Iron oxides can cause the stone to vary from buff or brown through to the deepest red. Grey colour stone is due to the presence of clay and green could indicate the presence of glauconite which contained potassium.

Sandstone is a natural material traditionally regarded as the building stone of the North. However, sandstone can be seen throughout the United Kingdom in many prestigious buildings from structures which form part of our heritage to modern office blocks.

Sandstone is traditionally used as a building material in many areas where it occurs locally particularly in Derbyshire, Yorkshire and the North East of England, Wales and Scotland. Many of the "stone cities" of the North derive their particular architectural character from the use of sandstone.

Most of the major sandstone quarries working today are located in the North of England, Derbyshire and Scotland. For flooring purposes, sandstones are also imported.

Granite

The term granite has been applied to almost any igneous stone that can retain a polish. True granites provide many of these stones but other types of igneous stone that may fall into this classification include syenites, gabbros, dolerites, and diorites. The metamorphic stones gneiss, schist and granulite are frequently also included in this ‘granite' classification.

The formation of these igneous rocks by the slow cooling of molten minerals such as quartz, feldspar and hornblende has resulted in a wide variety of colours and grain patterns.

In the United Kingdom the quarrying of granite is concentrated in a small number of locations. Those of particular importance may be found in Devon and Cornwall, Cumbria, at Peterhead and Aberdeen and on the east coast of Scotland.

Slate

Slate is found extensively, throughout the British Isles and has, for centuries, been a major source of building stone. Historically, and, in common with other stones, it was first used in and around the immediate areas of availability.

The term slate is often used to describe any rock that can be easily split into thin sheets, principally for roofing purposes. True slate is defined by the presence of a ‘slaty' cleavage; this allows the slate to be split at almost any point through the stone parallel to the cleavage plane. Most true slates are metamorphosed sediments, often formerly mudstones; however, some British "slates" are derived from volcanic ash sequences and are not true slates in the strict geological sense.