TOPIC 1 -ROCKS .pdf

TOPIC I ROCKS WHAT ARE ROCKS? -In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorised by the minerals included, its chemical composition, and the way in which it is formed...

TOPIC I ROCKS WHAT ARE ROCKS? -In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorised by the minerals included, its chemical composition, and the way in which it is formed HOW ARE ROCKS FORMED? -Rocks form the Earth's outer solid layer, the crust, and most of its interior, except for the liquid outer core and pockets of magma in the asthenosphere. The study of rocks involves multiple subdisciplines of geology, including petrology and mineralogy. It may be limited to rocks found on Earth, or it may include planetary geology that studies the rocks of other celestial objects. WHAT ARE THE THREE MAIN GROUPS OF ROCKS? -Rocks are usually grouped into three main groups: Igneous Rocks Sedimentary Rocks Metamorphic Rocks. 1 IGNEOUS ROCKS Igneous rock (derived from the Latin word igneus, meaning of fire, from ignis meaning fire)is formed through the cooling and solidification of magma or lava. This magma may be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition Igneous rocks are divided into two main categories: Plutonic or intrusive rocks result when magma cools and crystallises slowly within the Earth's crust. A common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, forming minerals such as pumice or basalt. About 65% of the Earth's crust by volume consists of igneous rocks. Of these, 66% are basalt and gabbro, 16% are granite, and 17% granodiorite and diorite. Only 0.6% are syenite and 0.3% are ultramafic. The oceanic crust is 99% basalt, which is an igneous rock of mafic composition. Granite and similar rocks, known as granitoids, dominate the continental crust. 2 SEDIMENTARY ROCKS Sedimentary rocks are formed at the earth's surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms or as chemical precipitates and organic growths in water (sedimentation).This process causes clastic sediments (pieces of rock) or organic particles (detritus) to settle and accumulate or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation at moderate temperatures and pressures (diagenesis). Sediment and the particles of clastic sedimentary rocks can be further classified by grain size. The smallest sediments are clay, followed by silt, sand, and gravel. Some systems include cobbles and boulders as measurements. About 7.9% of the crust by volume is composed of sedimentary rocks, with 82% of those being shales, while the remainder consists of 6% limestone and 12% sandstone and arkoses. Sedimentary rocks often contain fossils. Sedimentary rocks form under the influence of gravity and typically are deposited in horizontal or near horizontal layers or strata, and may be referred to as stratified rocks. 3 METAMORPHIC ROCKS Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism, meaning "change in form". Metamorphism is a profound change in the physical properties and chemistry of metamorphic rocks, which transform into various mineral types or forms. This process occurs at higher temperatures and pressures than Earth's surface, such as when continental plates collide. Metamorphic rocks, which make up 27.4% of the crust by volume, are divided into three major classes: contact metamorphism, pressure metamorphism, and regional metamorphism. The texture of metamorphic rocks is determined by the types of minerals present, with foliated rocks being primarily composed of lamellar minerals. The types of minerals present in metamorphic rocks are determined by their texture and the presence of lamellar minerals. Examples include schists, gneiss, slates, phyllites, mylonite, marble, soapstone, and serpentine. 4 BASALT Basalt is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. Basalt, a significant volcanic rock type, is found in the Solar System, forming basalt lava, which is observed in approximately 20 volcanoes annually. Basalt is used in construction (e.g., as building blocks or in groundwork), as cobblestones (made from columnar basalt), and to create statues. Heating and extruding basalt produces stone wool, which has the potential to be a great thermal insulator. 5 GRANITE Granite is a coarse-grained (phaneritic) intrusive igneous rock, primarily consisting of quartz, alkali feldspar, and plagioclase. It is formed from magma rich in silica and alkali metal oxides, which slowly cools and hardens underground. These rocks are classed according to the relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification), with real granite denoting granitic rocks high in quartz and alkali feldspar. Most granitic rocks contain mica or amphibole minerals, although some (known as leucogranites) have nearly no dark minerals. Granite is used as a pavement material. This is because it is incredibly resilient, porous, and requires less care. 6 PUMICE A pumice stone is a type of volcanic rock that forms when lava suddenly cools during an eruption. It’s porous and light and has a sponge-like appearance. Many industries use pumice as an abrasive, including health and beauty. Pumice is a volcanic stone made out of very coarse-textured volcanic glass, which may contain crystalline minerals. Pumice can be found wherever there is gas and water in a quickly cooling magma. Italy is the major producer of pumice, closely followed by neighbouring nations like Spain, Greece, and Turkey. Pumice has been utilised specifically in concrete as aggregate for the production of lightweight concrete. 7 OBSIDIAN Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian flows, formed from felsic lava, contain lighter elements like sodium. Their high viscosity prevents atom transport, impeding mineral crystal formation and rapid cooling, leading to the formation of natural glass. Obsidian may be used to create exceptionally sharp knives, and obsidian blades are a form of glass knife created from naturally occurring obsidian rather than manufactured glass. 8 DIORITE Diorite is an intrusive igneous rock created by the gradual cooling underground of magma (molten rock). It has a moderate silica content and a comparatively low alkali metal content. Its composition is somewhere between low-silica (mafic) gabbro and high-silica (felsic) granite. On the edges of continents, diorite is found in mountain-building belts known as orogens. Its composition is identical to that of andesite, a fine-grained volcanic rock that is also frequently found in orogens. The Inca civilization used diorite as a construction stone. It was employed by mediaeval Islamic builders to create water fountains in the Crimea. Diorite was later widely utilised as cobblestone, and numerous diorite cobblestone roadways can still be found in England and Guernsey today.Guernsey diorite was used on the stairs of St. Paul's Cathedral in London. 9 RHYOLITE Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite. Rhyolite is found along convergent plate boundaries, where a slab of oceanic lithosphere is subducted into the Earth's mantle beneath the overlying oceanic or continental lithosphere. It is sometimes the dominating igneous rock type in these environments. Rhyolite occurs more frequently when the overlying lithosphere is continental rather than oceanic. The thicker continental crust allows rising magma to discriminate and assimilate crustal rock. 10 ANDESITE Andesite is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the feldspar in the rock consisting of plagioclase. Notable stone masonry structures built with andesite include: 1. Sacsayhuamán citadel in Peru 2. Gate of the Sun in Bolivia 3. Borobudur in Java, Indonesia. 11 SANDSTONE Sandstone is a clastic sedimentary rock made up primarily of sand-sized (0.0625 to 2 mm) silicate grains held together by another material. Sandstones account for around 20-25% of all sedimentary rocks. Sandstone, composed of quartz or feldspar, is resistant to Earth's surface weathering and can be tan, brown, yellow, red, grey, pink, white, and black. Its colours are associated with certain regions, like the red rock deserts of Arches National Park. Sandstone, a prehistoric material, has been used for construction, decorative art, and tools worldwide. Orthoquartzite, a pure quartz sandstone with 90-95% quartz content, is proposed for Global Heritage Stone Resource nomination in Argentina. 12 LIMESTONE Limestone, a carbonate sedimentary rock, is primarily composed of calcite and aragonite minerals. It forms when these minerals precipitate from dissolved calcium in water, with biological processes being more significant for the last 540 million years. Sedimentary rock comprises 20%-25% carbonate, primarily limestone, with the remaining carbonate being mostly dolomite, a mineral rich in dolomite (CaMg(CO3)2). Magnesian limestone is an obsolete term. Limestone, a key raw material for lime production, is prone to acid rain, causing severe damage to artifacts and building surfaces, highlighting the need for preservation measures. 13 MARBLE Marble is a metamorphic rock composed of carbonate minerals, typically calcite or dolomite, recrystallized under heat and pressure, with a crystalline texture and typically not foliated. Marble, a type of metamorphosed limestone, is commonly used in stonemasonry for sculpture and construction, and is also used in stonemasonry for unmetamorphosed limestone. Construction marble, made from calcite, dolomite, or serpentine, is used in the dimension stone trade for building stone. Tennessee marble, a dense granular limestone, is a notable example. Ashgabat, Turkmenistan, has the world's highest concentration of white marble buildings. 14 ITALIAN MARBLE Italian marble has been a symbol of luxury and refinement, favoured for its exquisite beauty, durability, and sophistication in construction and decoration projects worldwide This natural stone is taken from Italy's mountains, specifically from Tuscany, Carrara, and Sicily. Italian Marble is made from limestone that has metamorphosed, producing a material that is denser, stronger, and more resistant to wear and tear than other forms of marble. Imported marble is a flexible material that can be used in a variety of applications, including floors, worktops, walls, and ornamental accents. It is valued for its visual appeal, sturdiness, and endurance. 15  With proper upkeep and care, marble may survive for decades, if not centuries, making it an excellent investment for anybody looking for high-quality, long-lasting materials. SOME TYPES OF ITALIAN MARBLE : a. Botticino Marble b. Carrara Marble c. Michelangelo Marble DIFFERENCE BETWEEN MARBLE AND ITALIAN MARBLE. 1. Italian marble, known for its elegance and delicate veining, is versatile and suitable for interior styles. Indian marble, on the other hand, offers a more subtle, earthy look with unique veins and patterns. 2. Italian and Indian marbles are both durable but softer, with Indian marble being more resistant to scratches and stains, requiring more maintenance for its appearance. 3. Italian marble is a luxury product used in high-end homes, hotels, and commercial buildings due to its quality, rarity, and transportation costs, while Indian marble is more affordable and popular for residential homes and offices. 16 4. Italian and Indian marble require regular maintenance, with Italian marble being more resistant to stains and scratches, while Indian marble requires more care and attention, using appropriate cleaning products and avoiding harsh chemicals. 17 ONYX Onyx is a parallel-banded chalcedony variety, while agate has curved bands and a wide range of colours Onyx, derived from Ancient Greek( ὄvυξ )meaning "claw" or "fingernail", can sometimes resemble a fingernail, with the English word "nail" cognate to the Greek word. Onyx has a long history in hardstone carving, jewellery, and intaglio and hardstone cameo engraved gems. It was used in Egypt as early as the Second Dynasty for pottery items and art deco sculptures. Brazilian green onyx was used in trays and pin dishes in Austria. Onyx was known to the Ancient Greeks and Romans and was used in various artificial treatment techniques. Mies van der Rohe used onyx slabs in Villa Tugendhat at Brno. The Hôtel de la Païva in Paris and the Mariinsky Theatre Second Stage in St. Petersburg also use yellow onyx in their décor. 18 SLATE Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from original shale-type sedimentary rock, composed of clay or volcanic ash, with foliation perpendicular to the direction of metamorphic compression. Slate, a type of stone, is formed through a process called "slaty cleavage" due to strong compression. This process creates flakes that regrow in planes perpendicular to the compression. Slates can also display fissility, forming smooth, flat sheets used for roofing and floor tiles. Slate is often grey, but can also be purple, green, or cyan. It's not to be confused with shale or schist. 19  Slate, a type of roof tile, has two lines of breakability: cleavage and grain. Its low water absorption index makes it resistant to frost damage and requires minimal processing. Natural slate is preferred by building professionals due to its beauty and durability. It can last several hundred years with minimal maintenance and is fire-resistant and energy efficient. Slate roof tiles are fixed with nails or hooks, with double nails in the UK and sarking boards in Scotland and Northern Ireland 20 GNEISS Gneiss is a common and widely distributed metamorphic rock formed by high-temperature and high-pressure processes on igneous or sedimentary rocks. It forms at higher temperatures and pressures than schist and typically has a banded texture with alternating darker and lighter bands without distinct cleavage Gneisses are common in the ancient crust of continental shields. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss. Gneiss has been utilised as a building material, namely Facoidal gneiss, which is widely used in Rio de Janeiro. Gneiss has also been utilised as a construction aggregate in asphalt pavement. 21 QUARTZITE Quartzite is a firm, non-foliated metamorphic rock that was once pure quartz sandstone. Sandstone is changed into quartzite through heating and pressure, which is typically associated with tectonic compression inside orogenic belts. Pure quartzite is normally white to grey, however quartzites can also be pink or crimson due to variable concentrations of hematite. Other minerals give rise to colours including yellow, green, blue, and orange. Quartzite is a decorative stone used in walls, roofing, flooring, and stairsteps, with increasing use in kitchen countertops and road construction. It is harder and more resistant to stains than granite. Quartzite, a silica form, poses a workplace concern due to its release of small, crystalline silica dust particles, a known human carcinogen, potentially leading to lung diseases like silicosis and pulmonary fibrosis. 22 SCHIST Schist is a metamorphic rock with a medium-grained texture, characterised by schistosity, characterised by easily visible mineral grains and high platy minerals like mica, talc, chlorite, and graphite interlaced with granular minerals. Schist, a type of rock formed during regional metamorphism, is a medium-grade metamorphism that can originate from various types of rocks, including sedimentary and igneous rocks. It is often rich in mica and is named after its protolith, such as schistose metasandstone. The name is often accompanied by the names of the constituent minerals, such as quartz-feldspar-biotite schist. Schist bedrock presents challenges for civil engineering due to its pronounced planes of weakness. 23  Schist is formed from shale or mud but at a much higher temperature than slate. Schist is not a very strong rock, so it is not often used as a building material. However it can be used for garden decoration, paving and sometimes sculpture. 24