Page 10 - Curriculum Visions Dynamic Book

Oxygen in minerals and rocks
Oxygen makes up about half of the mass (weight) of material in the Earth’s crust,
Most minerals are compounds of oxygen and the majority of these are silicates or oxides. In all silicates, more than half the atoms are oxygen. Together, silicon and oxygen comprise three- quarters of the mass of the Earth’s crust. This means that when you look at any soil or rock you are probably looking at a solid, locked-together mass of silicon and oxygen.
Silica
Silica is a molecule of one silicon atom and two oxygen atoms locked together by strong bonds. This unit forms the building block for many of the world’s minerals. In its pure form it makes up silicon dioxide, quartz, also known as silica, and the minerals that it forms are called silicates. It takes 18 million of these tiny units to make a piece of silicate 1 centimetre long.
Many of the world’s gemstones – such as sapphire, aquamarine and emerald – are silicates, combining metal ions with silica.
All the familiar building materials – glass, brick, pottery clay and even concrete – are also combinations containing oxygen and silicon.
Topaz
Topaz is a form of a silicate containing the metals aluminium and fluorine. It varies in colour and may be colourless, white, grey, yellow, orange, brown, light blue, light green, purple or pink. It is regarded as a gemstone.
Topaz crystal
 The structure of silica is very similar to diamond, with the silicon atoms packed tightly together. Four large oxygen atoms lie at the corners of a tetrahedron, almost entirely surrounding a smaller silicon atom. The electric charges between
the silicon and the oxygen atoms balance exactly, forming strong bonds. This structure makes, among other minerals, quartz, which is very stable and unreactive.
This is a model of part of a silica molecule. It is in the form of a four- cornered solid called a tetrahedron. This is the basic building block of most of the world’s minerals.
Oxygen
Silicon
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