Transcript Slide 1
PETROLOGY • TOPICS COVERED – Igneous rocks – Sedimentary rocks – Metamorphic rocks • TOPIC TO BE COVERED – Engineering properties of different types of rocks and its uses – Types of engineering tests performed on rocks GRANITE GRANITE • Plutonic igneous rock with holocrystalline and leucocratic type. • Acidic and oversaturated because of its silica content (72%) • Mainly consists of feldspar, quartz, mica and amphibole minerals. • Consists of 20% quartz, 65% alkali feldspar • Density 2.65-2.7 g/cm3 OCCURRENCE-STRUCTURE • Compact, dense, massive and hard rock. • Mural joints- (two sets vertical, one horizontalall mutually perpendicular) occurs in some. • Consists of rock into a number of rectangular blocks –quarrying. • Granites are unstratified PHYSICAL PROPERTIES-GRANITE 1. Massive un-stratified and dense 2. Interlocking texture-more strength 3. Equiangular or porphyritic texture (mosaic appearance) 4. Non permeable-will not become weak when dissolved in water 5. Rich in silica-resistant against weathering 6. Rich in minerals-resistant against abrasion 7. Presence of mural joints-easy for quarrying 8. Easily available 9. Having pleasing colour occurrence-decorative 10. Ability towards polishing 11. Resistance to fire and frost-minerals GRANITE-USES • Old times-antiquity Granite uses-Modern • • • • Sculpture and memorial Buildings Engineering Rock climbing DOLERITE o Dolerite is a hypabyssal rock. o It is found in sills and dykes. o It has dark gray or sometimes black texture. o Texture is medium to fine grained. o It is composed of Plagioclase, Augite and Iron Oxide with some Olivine. o Dolerite is an intermediate rock between Gabbro and Basalt. o As the texture increases in its coarseness, it approached Gabbro and as the texture becomes finer, it approaches Basalt. DOLERITE-PHYSICAL PROPERTIES 1. Having similar properties like granite but the only difference is colour (Pure black-highly demanded) 2. More fine grained-more stronger 3. Difficulty in quarrying-more tough 4. Springs and seepages are also occurs due to dolerite USES OF DOLERITE o Due to interlocking of crystals, the rock is very tough and is widely used as a road metal. o It has a quality of making firm grip with coal tar. o Extensively used as aggregate for concrete work. o In its unearthed state, Dolerite is one of the strongest building stone. BASALT BASALT o Formed by rapid cooling of basaltic lava exposed very near to the surface o On Earth, most basalt magmas have formed by decompression melting of the mantle. o The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the ocean ridges. MORPHOLOGY AND TEXTURES • Sub aerial eruptions • Columnar basalt • Submarine eruptions-pillow basalt 1.SUB AERIAL ERUPTIONS Basalt which erupts under open air (that is, sub aerially) forms three distinct types of lava or volcanic deposits: scoria; ash or cinder (breccia); and lava flows. Basalt in the tops of sub aerial lava flows and cinder cones will often be highly vesiculated, imparting a lightweight "frothy" texture to the rock. Basaltic cinders are often red, coloured by oxidized iron from weathered iron-rich minerals such as pyroxene. 2. COLUMNAR BASALT o During the cooling of a thick lava flow, contractional joints or fractures form. o If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it can't easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. 3. SUBMARINE ERUPTIONS-PILLOW BASALT o When basalt erupts underwater or flows into the sea, contact with the water quenches the surface and the lava forms a distinctive pillow shape, through which the hot lava breaks to form another pillow. o This "pillow" texture is very common in underwater basaltic flows and is diagnostic of an underwater eruption environment when found in ancient rocks. o Pillows typically consist of a fine-grained core with a glassy crust and have radial jointing. The size of individual pillows varies from 10 cm up to several meters. BASALT-PHYSICAL PROPERTIES AND USES • Refers to massive, fine grained melanocratic rock • Massive basalts are highly durable and strongest (high load carrying capacity) • More fine grained then dolerite • Used as a building stone • Used as a road metal SAND STONES • 15% of sedimentary rocks represented by sand stones. • Sand grains in sand stones are mostly quartz • Colourless, fresh and with vitreous lustre • Based on the size of sand grains, the sand stones may be coarse grained, medium grained or fine grained. • Present in rounded or sub rounded or angular in shape. • Occurs in different color's i.e. white, red, brown, yello and green. • Colour is mainly due to its cementing material (mostly quartz) – Red/yellow/brown – ferruginous – White - reacts with acid –cementing material calcium carbonate – Dirty pale – mostly clay as cementing material – White or dirty white with hard material property – silica as cementing material SAND STONES-TYPES I BASED ON GRAIN SIZE 1. Coarse grained – 1 to 2 mm 2. Medium grained – 0.5 mm 3. fine grained – less than 0.5 mm SAND STONES-TYPES II. BASED ON THE COMPOSITION 1. Ferruginous – Cementing mixture oxides and hydroxides 2. Calcareous – cementing mixture calcium carbonate 3. Argillaceous – cementing material clay 4. Siliceous – cementing material silica 5. Glauconitic – cementing material glauconitic SAND STONES-TYPES III BASED ON MINERAL CONTENT – Arkose – rich in feldspar – Graywacky - dark in colour and rich in clay – Micaceous sandstone – mica flakes content SAND STONES-TYPES IV BASED ON SHAPE OF GRAINS Grit – coarse grained, angular V BASED ON STRUCTURE – Flaggy – thin slab like structure – Free stone – massive, uniform and thick bedded – Ganister – fine grained – Ortho quartzite – siliceous stone with negligible porosity