Rock formation

A short introduct

1. Rock Formation Introduction for Stonemasons Stonemasonry Department 2012

2. The Rock Cycle Image by British Geological Survey

3. Sedimentary Rock Sedimentary rock is formed by the deposition of multiple layers of sediment in a process known as lithification . Once deposited, the weight of new layers compacts previous layers with such a force that they fuse together. Over millions of years the layers continuously build up before geological processes leave them exposed and accessible for quarrying operations.   Compacted sediment New layers of sediment Rock bed Water New layers of sediment

4. Deposition of Sediment Image by British Geological Survey Three methods of sediment disposal are weathering, erosion and transport ( streams, rivers, glaciers and wind)

5. Deposition of Sediment Image by British Geological Survey

6. Types of Sedimentary Rock Sandstone is formed by the lithification of sand sized minerals and rock grains which have been transported and deposited. Most sandstones contain high levels of quartz or feldspar as these are the most common minerals in the earths crust. Limestone is predominantly formed from the remains of dead marine organisms which contain calcium carbonate. Having died and fallen to the bottom of the ocean, these creatures are compacted over millions of years to form limestone. Images by British Geological Survey

7. Sedimentary Stone Variations The variations in sedimentary stone colours and textures can be seen in the image above. Note that this is only a small selection of British stones . The selection of stone has been sourced from Tradstocks.co.uk  

8. Natural Bedding When stone is built on its natural bed its sediment remains on the same plane as when it was formed. This allows the stone to maximise its compressive strength and reduces weathering and erosion. Most stones on a building are built on natural bed ( ashlar , rybats , quoins, lintols etc). F

9. Joint/Edge Bedding When stone is built on its edge bed its sediment faces at 90 degrees to the plane as when it was formed. This bedding plane is used for arch stones and for overhanging stonework such as sting courses, band courses, cornices and in freestanding work such as ballusters . F

10. Face Bedding When stone is built on its face bed its sediment faces at 90 degrees to the plane as when it was formed and each layer of sediment is fully exposed. This bedding plane is normally avoided as it is particularly susceptible to rapid erosion and has lower compressive strength than natural bedding. It can be used on ballusters and finnials . F

11. Building to the Correct Bedding This image shows ashlar stonework built on a combination of natural and edge bedding plane.

12. Igneous Rock Solidified molten rock Rock bed Water Molten rock from volcanic activity Igneous rock is formed by molten rock (magma) which has cooled and solidified or by ash produced by a volcanic eruption. There are various forms of igneous rock some of which are very hard and durable (granite) whilst others are lightweight and brittle (pumice). The rock can be formed due to volcanic eruptions or less visible forms of volcanic activity (in underground magma chambers).  

13. Formation of Igneous Rock Image by greenanswers.com

14. Types of Igneous Rock Granite is formed by the cooling of magma and contains a minimum of 20% quartz. It is a very dense stone and has exceptionally high compressive strength which makes it particularly suitable for plinths. Tuff is formed from the sedimentary compaction of volcanic ash and so is a lightweight rock which is suitable either as a building material or as a pozzolan which is combined with a lime mortar for building.

15. Metamorphic Rock Magma Sedimentary rock New layers of sediment Top layers of sediment Compacted and heated sediment Metamorphic rock is rock which has been subjected to intense heat and pressure and through a metamorphic process has changed into another type of rock. The two most commonly used metamorphic rocks in the stonemasonry industry are marble (limestone) and slate (shale).  

16. Types of Metamorphic Rock Slate is formed from the metamorphisism of shale and tends to retain a heavy lithification which makes it easy to split. Due to its low porosity, slate is often used as a roofing material. Quartzite is metamorphisised sandstone. In the image above (centre) it is clear that the bedding plane has been radically altered due to intense heat and pressure. Marble is metamorphisised limestone which has been crystallised. This type of stone is commonly used for ornamental stonework such as statues and intricate carving work.

17. Developed by The Stonemasonry Department City of Glasgow College 2012