Types of Rocks IGNEOUS ROCK

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Kristina Williamson
5 years ago
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1 TOPIC FOUR 1

Types of Rocks Rocks are not all the same!

Sometimes the magma cools inside the earth (INTRUSIVE) and other times it erupts onto the surface from volcanoes (in this

Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.

of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment.

2 Types of Rocks Rocks are not all the same! The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed. IGNEOUS ROCK Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth (INTRUSIVE) and other times it erupts onto the surface from volcanoes (in this case, it is called lava) (EXTRUSIVE). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock. Examples of this rock type include basalt, obsidian and pumice SEDIMENTARY ROCK Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils. Examples of this rock type include conglomerate and limestone. 2

Metamorphic Rock Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing).

Examples of this rock type include gneiss, marble and granite.

The different rock layers resulted from different environments and geological times in which the sediments and fossils were deposited.

3 Metamorphic Rock Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface. Examples of this rock type include gneiss, marble and granite. Maltese Rock Layers The Maltese Islands started to form around 30 to 25 million years ago when sediment and fossils were deposited on the bottom of the sea. The different rock layers resulted from different environments and geological times in which the sediments and fossils were deposited. Around 10 million years ago, these rock years rose to the surface due to African plate and the Eurasian plate moving towards each other causing the sediment in between to uplift. Therefore, all of the Maltese rock types are sedimentary. The image of the Maltese Islands,on the next page is a geological map. Each colour shows a particular type of rock that makes up the islands. The Maltese Islands are made up of 5 different rock types. These are namely; Upper Coralline Limestone, Greensand, Blue Clay, Globigerina Limestone and Lower Coralline Limestone. 3

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This image shows the locations on Malta where this type of rock may be found in Maltese it is called l-qawwi ta' fuq. It is found on top of hills and plateaus in Malta and Gozo.

It is also porous, which means that it lets water pass through it. Upper Coralline Limestone This image highlights the locations on Malta where this type of rock may be found.

Greensand is known to contain a lot of marine fossils such as that depicted in this photo. Greensand This image shows the locations on Malta where this type of rock may be found.

5 This image shows the locations on Malta where this type of rock may be found in Maltese it is called l-qawwi ta' fuq. It is found on top of hills and plateaus in Malta and Gozo. It is quite a hard rock having a white and/or grey colour. It is the youngest rock found on the Maltese Islands meaning that it was the last to form. It is also porous, which means that it lets water pass through it. Upper Coralline Limestone This image highlights the locations on Malta where this type of rock may be found. In Maltese we find this rock named as il-gebla is-safra. It is a very thin layer of rock usually having an orange colour. It is highly porous and it easily crumbles into sand. Greensand is known to contain a lot of marine fossils such as that depicted in this photo. Greensand This image shows the locations on Malta where this type of rock may be found. Blue Clay is known as it-tafli in Maltese. As its name implies it has a bluish shade. It is also a soft rock that erodes quickly. It is porous but it is not permeable. Blue Clay was commonly used for pottery making. However, this tradition has diminished. Blue Clay 5

Globigerina Limestone This image shows the locations on Malta where this type of rock may be found. In Maltese it is found as Franka.

It is used mainly for buildings and making of sculptures.

Lower Coralline Limestone is called il-qawwi t'isfel or Zonqor in Maltese. It is the oldest rock type of the Maltese Islands.

6 Globigerina Limestone This image shows the locations on Malta where this type of rock may be found. In Maltese it is found as Franka. It is softer than Coralline Limestone but it is harder than Blue Clay and Greensand. It is a porous rock usually having a white/yellow colour. It is used mainly for buildings and making of sculptures. Lower Coralline Limestone This image shows the locations on Malta where this type of rock may be found. Lower Coralline Limestone is called il-qawwi t'isfel or Zonqor in Maltese. It is the oldest rock type of the Maltese Islands. This means that it was the first to form. It is a hard rock, porous and has a white/grey colour. The Lower Coralline Limestone is mainly used for road surfacing and in concrete mixtures. The Maltese rock sequence is relatively simple being divided into five main layers (se picture). 6

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4.1 Act 2 Rock Cycle: Interactive Website Worksheet

Name Date Core 4.1 Act 2 Rock Cycle: Interactive Website Worksheet Directions: Go to the website Interactives Rock Cycle. http://www.learner.org/interactives/rockcycle/index.html Follow the directions