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 horizontal-

all 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

DOLERITEo 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 ERUPTIONSBasalt 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 BASALTo 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 BASALTo 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

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

SAND STONES-TYPES