Page 117 - Active Science 5 Ebook and Activity

T ypes of Rocks

Rocks occur in many varieties and colours. Rocks can be classified into three main types
– igneous, sedimentary and metamorphic.

Igneous Rocks
Volcanic eruptions result in the flow of magma on the surface of the earth. Magma is the
molten rock. The magma flowing out of the volcanic holes onto the surface of the earth is
called lava. After sometime, this lava cools down and hardens to form rocks. The rocks

formed by the hardening of lava are called igneous rocks. The term igneous rocks
has been derived from the Latin word ignis.

Some minerals like mica, magnesium, etc., are present in the igneous rocks. There are
three kinds of igneous rocks.

1. Granite: When a rock is formed due to
the slow cooling of lava, it is hard in

structure. It is called granite. Granite
comes in many patterns and colours,
i.e., it varies from grey to pink. Mica,
feldspar and quartz are three main

minerals present in granite. Granite

Granite is used on kitchen counters for
flooring, etc. It is also used in making
buildings.

2. Obsidian: It is formed by quick cooling
of lava. It is black, smooth and glassy.
It is also called volcanic glass.

It is used in making jewellery and
ornaments. Obsidian

3. Pumice: Pumice is also formed by

quick cooling of lava. Lava contains a
lot of dissolved gases. As the lava cools,
the gases trapped in it escape, forming

holes. This makes the rock light. It is
grey or creamish in colour.

Pumice is used as a scrubber, for making
light building material, etc. Pumice

117
Active Science-5