NewsELA_How_To_Identify_Rock_Types.pdf - How to identify...

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How to identify the three major types of rocks
Image 1. This is an outcrop of igneous rock in Iceland. Igneous rock is created by volcanic activity. Photo by: Phil Degginger/Science Source
In geology, pictures of rocks can be used to help you best determine which of the three major types
a particular rock belongs to: igneous, sedimentary or metamorphic.
By comparing your rock sample with photographic examples, you can identify key characteristics,
such as how the rock was formed, what minerals and other materials it contains, and where the
rock may have come from.
Sooner or later, you're bound to encounter hard, rock-like substances that aren't rocks. Such items
include man-made substances like concrete and bricks, as well as rocks from outer space (such as
meteorites) that have dubious origins.
Before beginning the identification process, make sure that your sample has been washed to
remove dirt. You'll also want to make sure you have a freshly cut surface so you can identify color,
grain structure, stratification, texture and other characteristics.
Igneous Rocks
By Andrew Alden, ThoughtCo., adapted by Newsela staff on 09.19.19
Word Count 819
Level MAX

This article is available at 5 reading levels at .
Igneous rock is created by volcanic activity. These
rocks come from magma and lava as they cool and
harden. Igneous rock is most often black, gray or
white. It often has a baked appearance.
Igneous rock may form crystalline structures as it
cools. This gives it a granular appearance; if no
crystals form, the result will be natural glass.
Examples of common igneous rock include: basalt,
granite and obsidian.
Basalt is formed from low-silica lava. Basalt is the
most common type of volcanic rock. It has a fine grain
structure and is usually black to gray in color. Another type of igneous rock is granite. This rock
may range from white to pink to gray, depending on the mix of quartz, feldspar and other minerals
it contains. It is among the most abundant type of rock on the planet. Obsidian is a type of igneous
rock that is formed when high-silica lava cools rapidly. This forms volcanic glass. It is usually