These are great masses of hard materials that make up the outer part of the earth. They are aggregate of minerals which may occur as single or in groups of minerals. A mineral is a naturally occurring chemical substance hat is neither a plant nor an animal. Geologists divide all rocks into main groups. When geologists speak of rocks, they usually do not mean a small stone. They mean the great mass that make up a mountain or that underlies a large region.
1. IGNEOUS ROCKS (from Latin igneuos – fire).These are formed from rock materials so hot that it was liquid. Most of the liquid rock material cooled and hardened below the surface of the earth. Some of the liquid rock broke through the surface, flowed out and then hardened. Igneous rocks underlie all other rocks of the earth. It forms the base of the continent and the cores of mountains. It lies beneath the sediments of the oceans. An igneous rock mass that can be seen on the surface may once have been the core of the mountain. It may be rock that reached the surface in a molten state. But, whenever it was formed deep within the earth or on the surface, all igneous rock was once liquid. 2 Kinds of molten materials a. Magma – are liquid rock that lies in underground pockets in huge quantities. It is found 60 to 200 kilometers below earth’s surface, at or near the crust / mantle boundary. b. Lava – are magma that moves upward to the earth’s surface. They are released during volcanic eruptions or flows out through fractures onto earth’s surface.
2 General Types of Magma • Basaltic magma – flows readily and forms thin layers of dark colored lava that cover large areas. This magma makes up much of the ocean floor. Temperatures of basaltic magma range from 900 to 12000 at the surface. IT contains a high percentage of iron and magnesium. The presence of these elements produces igneous rocks that are generally quite dense and dark in color. • Granitic magma – is thick and stiff due to its high silica content. Its temperature is generally below 8000C at the surface. It contains a high percentage of aluminum and potassium or sodium. These produce less dense, lighter-colored igneous rocks.
2 Kinds of Igneous Rocks as to Form: • Intrusive igneous rocks - formed when magma forces its way into pre-existing rocks and solidifies slowly. Solidification of these rocks occurs inside the earth. The rock contains iron -magnesium minerals. • Examples: • - peredotite – is composed of all living. • - gabbro basalt – is formed after more coaling of the peredotite. • - diorite – is made of sodium with some iron- magnesium. • - granite – the last rock to formed which contains quartz with small amount of sodium.
INTRUSIVE INGEOUS ROCKS PEREDOTITE GABBRO BASALT DIORITE GRANITE
Extrusive igneous rocks (fine - grained rocks) – formed when magma goes out into the earth’s surface and cools there rapidly into fine crystals. They may be blown out when volcanoes erupt or may come out quietly from cracks of rocks. • Examples: • - basalts – are dark in dense and can be recognize even if the • minerals cannot be identified. • - rhyolite – fine – grain equivalent to granite. • - andesite – is the fine - grain equivalent to diorite.
EXTRUSIVE INGEOUS ROCKS ANDESITE BASALT RHYOLITE
2. SEDIMENTARY ROCKS – are made of loose Earth materials called sediments. These rocks are formed from weathered igneous, metamorphic or other sedimentary rocks that are found on the earth’s surface. • Many sedimentary rocks are deposited in a series of layers which are recognized by differences in color, grain, size, and composition. The oldest layer at the bottom and the youngest bed on top. Fossils, especially of the marine life, are common in sedimentary rocks. Fossils, are the remains on traces of once living organism preserved in the earth’s rocks. Bones, shells and prints of plants and animals may be preserved as fossils. • Features of Sedimentary Rocks: • Ripple marks – are wavy features of some sand stone which are common in • beaches. • Concretions– are ball – like objects or irregularly shaped masses of cementing • material that are collected around a nucleus. • Geodes – are ball – like objects found in some sedimentary rocks.
Classification of Sedimentary Rocks: • 1. Clastics – are made from fragments of rocks, minerals and broken shells. • - Conglomerate – are mixtures of rounded pebbles of any kind and • shape. Clay and sand grains also may be present. Less than 2mm in • diameter. • - Breccia – similar to conglomerate except that its fragments are sharp, • angular pieces. Less than two mm in size. • - Sandstone – usually consist of small quartz grains, but maybe • composed of calcite, feldspar, or pieces of other rocks, sandstone feel • gritty and the grains that compose them are easy to see 0.0625 to 2mm • in size. • - Siltstone – is like sandstone but with much smaller grains which can be • felt but can be seen only with magnification 0.004 to 0.06mm. • - Shale – is made of thin layers of clay and sized particles that are too • small to be seen without magnification.
CLASTICS SEDIMENTARY ROCKS SANDSTONE BRECIA CONGLOMERATE SHALE SILTSTONE
2. Non – clastics – are sedimentary rocks that are deposited from solution or by organic process. • - Limestone – composed of calcite (CaCO3) • - Flint or Chert – made of silica • - Rock Salt – made of halite • - Rock Gypsum or Alabaster – made of gypsum • - Coal – fragments of plants or carbon compounds.
NON-CLASTICS SEDIMENTARY ROCKS FLINT OR CHERT LIMESTONE ROCK GYPSUM OR ALABASTER ROCK SALT COAL
3. METAMORPHIC ROCKS – are formed beneath the surface of the earth by the alteration of pre-existing igneous or sedimentary rocks. Alteration maybe due to high temperature, various chemical substances or a combination of pressure and shearing stresses caused by the movement of the earth’s crust. Meta is a Greek word, meaning to transform or change. • Classification of Metamorphic Rocks: • 1. Foliated rocks – are banded rocks that show layers • a. Slates – are finely foliated and tend to split also along the parallel lines into plates of uniform thickness. They are made from shale and break into very thin slabs which can be used as roofing materials and flagstones. Blackboards of many classrooms are used to be made of shale. • b. Phyllites – show foliation midway between that of schists and shale.
c. Schists – are rocks that show some internal change and definite foliation. The most common metamorphic rocks. • d. Gneisses – are the result of high temperatures and pressure. • 2. Non – foliated – are massive rocks and lack banding. These rocks usually contain only one mineral and have undergone internal changes. • a. Marble - is a metamorphosed limestone. Its crystals are harder • and larger than limestone. • b. Quartzite – forms from the sedimentary rock sandstone. • c. Serpentinite – has a marble streaks formed from a parent rock • that contains calcium.
FOLIATED METAMORPHIC ROCKS SLATES PHYLLITES SCHIST Gneisses
NON-FOLIATED METAMORPHIC ROCKS MARBLE QUARTZITE SERPENTINITE
Rock Cycle Concept This refers to the forming of earth materials into new rocks by responding to changing environment. Records indicate that the responses and adjustments have continued throughout the entire history of the earth. Igneous rocks become transformed to sedimentary rocks can be metamorphosed together with igneous rocks and metamorphic rocks may melt to form magma. Crystallization of magma will produce igneous rocks thus the cycle continues. Any type of rock can be weathered or eroded. Igneous rocks sometimes are metamorphosed without passing through a sedimentary stage. However, sedimentary rocks cannot be transformed to igneous rocks.