IC. Rocks, Minerals, Elements (and Crystals and Glass)

Rocks are composed of minerals, the hard, stable crystals and glasses that make up the Earth are called minerals. Most of the hard stuff on the surface of the earth is rock. We use many products made of rock, including slate for roofing and marble for building interiors.

Minerals are made up of one or more one element (one kind of atom) and can exist in a pure form, like diamonds and gold. Most are combinations of elements.

In fact, there are over 3000 different types of minerals. Amazingly, most of the Earth's crust (99%) is made of just ten types of minerals (the most common being feldspar and mica).

Granite ROCK, for example, is made of 3 MINERALS - each with their unique combination of ELEMENTS

The mineral feldspar is made of the elements silica, oxygen, calcium, sodium, and potassium.

The mineral mica is made of the elements potassium, aluminum, silica, and oxygen.

The mineral quartz is made only of quartz.

Crystals are a form of minerals in which the atoms have had time to assemble in an orderly way.

Large crystals are often formed underground, where they can grow slowly, atom by atom, undisturbed. Small crystals can be formed quickly.

Glass has atoms arrange in a less orderly way.

Elements -- Percent of Earth's Crust by Weight

Oxygen (O) 46.0%

Silicon (Si) 27.7%

Aluminum (Al) 8.1%

Iron (Fe) 5.0%

Calcium (Ca) 3.6%

Sodium (Na) 2.8%

Potassium (K) 2.6%

Magnesium (Mg) 2.1%

Look at the list above of the key elements of the Earth's crust. Which two elements make up most of the crust?