Geology of Building Stones

Building Stones

• Rocks are classified into three major categories: Geological, Physical, and Chemical.
• Geological rocks are further broken down into Igneous, Sedimentary, and Metamorphic.
• Physical classification includes Stratified, Un-Stratified and Foliated.
• Chemical classification includes Siliceous, Argillaceous, and Calcareous.
• Examples of igneous rocks are Vesicular basalt and Red granite.
• Examples of sedimentary rocks are Limestone and Sandstone.
• Examples of metamorphic rocks are Gneiss and Marble.

Geological Composition

• Igneous rocks form from cooled volcanic lava (magma). Examples include basalt and granite.
• Sedimentary rocks are formed from the gradual accumulation of disintegrated rocks. Examples include sandstone and limestone.
• Metamorphic rocks are produced by the transformation of other rocks due to heat and pressure. Examples include gneiss and marble.

Physical Composition

• Stratified rocks have distinct layers that can be separated, like slate, sandstone, and limestone.
• Un-stratified rocks lack distinct layers, like granite, basalt, and trap.
• Foliated rocks, found in metamorphic rocks, have a tendency to split along a certain plane/direction, known as S-taconite.

Chemical Composition

• Siliceous rocks contain primarily sand or silicates (SiO2), such as quartz, sand, granite, and basalt.
• Argillaceous rocks are mainly composed of alumina (Al2O3) and clay minerals, including slate and laterite.
• Calcareous rocks contain calcium carbonate and lime, such as limestone, marble, and dolomite.

Quarrying of Stones

• Quarrying is the process of extracting stones from rock beds.
• A quarry is the place where stones are obtained.
• Methods of quarrying include digging/excavating, heating, wedging, and blasting.

Selection of Quarrying Sites

• Criteria for selecting quarrying sites include sufficient quality, proper transportation, affordable labor, proper drainage, and avoiding permanent structures.

Methods of Quarrying

• Digging/Excavating: Using tools like crowbars to extract stones.
• Heating: Heating rock surfaces to cause unequal expansion and fracturing.
• Wedging: Splitting rocks using wedges at cleavage planes or seams, particularly useful for soft rocks.
• Blasting: Employing explosives for quarrying hard rock, following safety procedures such as carefully done tramping.

Quarrying Tools

• Specific tools are used for different quarrying techniques, including wedges, hammers, drills, jumpers, and chisels.

Precautions During Quarrying

• Blasting procedures are to be conducted during appropriate times, with safety zones clearly marked, and appropriate first aid facilities available.
• Strict adherence to safety guidelines, including proper storage of explosives and use of appropriate protective gear (rubber gloves), is crucial.
• Proper record-keeping in relation to the explosives and quarrying activities is necessary.

Explosives in Quarrying

• Various explosives are used in quarrying, including granulated powder, nitroglycerine dynamites, and ammonia dynamites.
• The choice of explosive depends on the specific conditions and properties of the rock to be extracted.

Dressing of Stone

• Methods for dressing stones include pitched faced, hammer dressed, rock faced, rough tooled, punched dressed, and fine tooled.

Methods of Dressing and Polishing Stones

• Methods such as applying linseed oil (raw or boiled) and solutions of alum and soap can be employed to protect the dressed stones.

Treatments for Stone Decay

• Barium hydroxide (baryta), used for calcium sulphate based decay.
• Paraffin, used as a paint medium.
• Paint, does change color.
• Coal tar, can harm some types of stone.

Artificial Stones

• Definition: Building materials made with cement, sand, and crushed stone.
• Properties: Molded into different forms, and reinforced to enhance strength and desired finish.
• Types: Concrete blocks, ransom stone, Victoria stone, bituminous stone, imperial stone, artificial marble, garlic stone.

Tests on Rocks

• Representative samples collected from different strata, at least 25kg in weight, and free from seams or fractures.
• Test pieces should be in a certain size (cm in size).

Simple Field Tests

• Water Absorption: Measures the amount of water absorbed by a sample of stone in 24 hours (Water absorption should not exceed 0.6%).
• Smith's Test: Used to assess stone durability or weathering quality, by submerging the stone in water for 24 hours and observing if the water turns cloudy, good; muddy, the stone contains earthy substances.

Laboratory Tests

• Attrition Test: Determines rate of wear of stones, conducted in a machine.
• Crushing Test: Measures the compressive strength of the stone using a compression testing machine.
• Freezing and Thawing Test: Evaluates the durability of the stone subject to freeze-thaw cycles.
• Hardness Test: Evaluates resistance to abrasion by rubbing a sample against a steel disc.
• Impact Test: Measures impact resistance useful in runways or airports.

Microscopy Test

• Examines mineral constituents, grain size, texture of the stone, cementing materials, and presence of harmful materials.