9781422283691

Rocks and Minerals

Many rocks are born   in fiery volcanoes   or deep undergound. The Earth’s crust is made up of many different kinds of rocks. They vary widely in content, color, hardness, and density. They are made up of different chemical compounds, or minerals . In some, the minerals are too small to be seen. In others, the minerals show up as colored specks or crystals. Quartz, or silica, is one of the most common minerals found in rocks. Quartz is the chemical silicon dioxide, a combination of the elements silicon and oxygen—the two most common elements in the Earth's crust. Many other minerals, called silicates, contain the same two elements and are found widely in rocks. ∆ Minerals are found in rocks in a variety of different shapes and colors. Galena (below) often forms shiny crystals with square faces. Malachite (below right) is a beautiful green color.

∆ The red-hot lava flows from volcanoes, destroying everything in its path.

Crystal clear You can grow your own crystals from bath salts, baking soda, or alum, which you can buy from a drugstore. Add the substance to hot water and stir. Keep adding it until no more will dissolve. Let the solution cool. Dangle a piece of thread into it and leave for several days. Crystals will grow on the thread.

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