PETROLOGY

1. PETROLOGY

2. 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

3. GRANITE

4. 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

5. OCCURRENCE-STRUCTURE • Compact, dense, massive and hard rock. • Mural joints- (two sets vertical, one horizontal-all mutually perpendicular) occurs in some. • Consists of rock into a number of rectangular blocks –quarrying. • Granites are unstratified

6. PHYSICAL PROPERTIES-GRANITE • Massive un-stratified and dense • Interlocking texture-more strength • Equiangular or porphyritic texture (mosaic appearance) • Non permeable-will not become weak when dissolved in water • Rich in silica-resistant against weathering • Rich in minerals-resistant against abrasion • Presence of mural joints-easy for quarrying • Easily available • Having pleasing colour occurrence-decorative • Ability towards polishing • Resistance to fire and frost-minerals

7. GRANITE-USES • Old times-antiquity

8. Granite uses-Modern • Sculpture and memorial • Buildings • Engineering • Rock climbing

9. DOLERITE • Dolerite is a hypabyssal rock. • It is found in sills and dykes. • It has dark gray or sometimes black texture. • Texture is medium to fine grained. • It is composed of Plagioclase, Augite and Iron Oxide with some Olivine. • Dolerite is an intermediate rock between Gabbro and Basalt. • As the texture increases in its coarseness, it approached Gabbro and as the texture becomes finer, it approaches Basalt.

10. DOLERITE-PHYSICAL PROPERTIES • Having similar properties like granite but the only difference is colour (Pure black-highly demanded) • More fine grained-more stronger • Difficulty in quarrying-more tough • Springs and seepages are also occurs due to dolerite

11. USES OF DOLERITE • Due to interlocking of crystals, the rock is very tough and is widely used as a road metal. • It has a quality of making firm grip with coal tar. • Extensively used as aggregate for concrete work. • In its unearthed  state, Dolerite is one of the strongest building stone.

12. BASALT

13. BASALT • Formed by rapid cooling of basaltic lava exposed very near to the surface • On Earth, most basalt magmas have formed by decompression melting of the mantle. • The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the ocean ridges.

14. MORPHOLOGY AND TEXTURES • Sub aerial eruptions • Columnar basalt • Submarine eruptions-pillow basalt

15. 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.

16. 2. COLUMNAR BASALT • During the cooling of a thick lava flow, contractional joints or fractures form. • 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.

17. 3. SUBMARINE ERUPTIONS-PILLOW BASALT • 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. • This "pillow" texture is very common in underwater basaltic flows and is diagnostic of an underwater eruption environment when found in ancient rocks. • 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.

18. 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

19. 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

20. 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

21. SAND STONES-TYPES II. BASED ON THE COMPOSITION • Ferruginous – Cementing mixture oxides and hydroxides • Calcareous – cementing mixture calcium carbonate • Argillaceous – cementing material clay • Siliceous – cementing material silica • Glauconitic – cementing material glauconitic

22. 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

23. 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