Page 74 - Journeys Through Society-7
P. 74
Limestone is a sedimentary rock formed by the
sediments of corals and seashells.
Rock salt is formed when soluble substances in water
settle down at the bottom of a lake or sea, becoming
hard under the pressure of the water above it. Coal is a
sedimentary rock formed when wood gets buried
inside the layers of the soil.
Dolerite
Sandstone Limestone Coal
crystals because they cool fast due to exposure to the
Earth's surface. Basalt and Pumice are two examples Metamorphic Rocks
of such rocks. Metamorphic rocks
are those that have
been subjected to
intense heat and
pressure for a long
time. Under such
conditions, these
Basalt Pumice rocks undergo a Diamond is a metamorphic rock.
Sedimentary Rocks complete change in
Sedimentary rocks are made up of fragments and their physical and chemical characteristics. This
sediments of other rock material that get cemented change or metamorphosis they undergo is the reason
together. They are a mixture of mud, sand and debris they are termed as metamorphic rocks. Shale is
layered together. metamorphised into slate, limestone into marble and
Since these rocks are not very hard, they get worn sandstone into quartzite.
down by the elements of nature. The worn-down
material is transported by wind, rivers and glaciers
and deposited elsewhere, where they once again form
sedimentary rocks.
Slate Marble Quartzite
Rock Cycle
The rock cycle describes the transition that the three
types of rocks undergo. All types of rocks get altered or
destroyed when they are forced out of their
equilibrium conditions.
The continual cycle that involves the process of
destruction and recreation of rocks is known as the
Sedimentary rocks
rock cycle. Sediments from water bodies form
Sandstone is formed from grains and sediments of a sedimentary rocks which are then crushed at the foot
pre-existing rock called the parent rock which has of mountains. This leads to the formation of
undergone physical weathering. metamorphic rocks. Sedimentary rocks may melt due
74
