Types of Rocks Pt. 2: The Layered Ones

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In part 1 of this article we discussed fiery liquid rocks, like lava. However, most of the earth’s crust is covered by a layer of sand and mineral fragments, or sediments. In many places, heat and pressure have compacted these sediments into solid rock. This is called sedimentary rock.

Over 75 percent of the earth’s surface is covered in sedimentary rock. You can recognize sedimentary rocks by the horizontal lines marking the boundaries between layers of hardened sediment.

Sandstone

Sandstone is a rough, crumbly rock that contains bits of quartz sand that have been fused together into rock. It is sometimes used for making glass. The outer walls of many old buildings are made of sandstone.

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Shale

Shale is formed from mud or clay that is made up of much smaller particles than sand, and is often found in layers of sandstone or limestone. It can easily be broken and ground up for use in making bricks.

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Crystal Halite / Rock Salt

Crystal halite, or rock salt, is mined and can be used in many ways, such as making chemicals, tanning leather, and salting roads in the winter.

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Chalk

Chalk is the cemented skeletons of microscopic sea animals. It is a soft, white rock used in the classroom to write on chalkboards, although most classroom chalk today is man-made. The famous White Cliffs of Dover are made of chalk.

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I did not have time to talk about more than a few, so I’m saving them for the next part.

Honorable Mentions

  • Conglomerate
  • Breccia
  • Reef Limestone
  • Shelly Limestone
  • Coal

<< Part 1 | Part 3 >>

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