Lithosphere: Part 1

Chapter 6 part 1
The Lithosphere
- The lithosphere is the hard shell of the Earth, consisting of the crust and the topmost part of the upper mantle.
This hard shell covering our planet is only about a hundred kilometres thick on average. The Lithosphere contains minerals and rocks that have been essential to the development of human civilization. It is the source of building materials, metals of all kinds and even precious stones for jewellery.

- Minerals are solid inorganic substances with clearly defined composition and properties. Minerals must exist naturally on Earth; they cannot be manufactured. Most minerals have an ordered atomic structure: their atoms are organized in the form of identically shaped crystals.
Because minerals are consistently made up of the same elements, forming crystals of a specific shape, minerals exhibit certain well-defined properties, such as hardness, transparency, colour and streak. More than 4000 differnet minerals are known to exist on Earth.



Mineral Classification:Geologists classify minerals according to their properties such as colour, streak, transparency, and hardness.

* COLOUR *The element that gives them their colour is part of their chemical composition. They are called idiochromatic minerals. Other minerals may vary in colour, so they are described as allchromatic. If they were chemically pure, allochromatic minerals would be colourless, but minute quantities of impurities give them different colourings.* TRANSPARENCY *Transparency is the property by which a substance allows light to pass through it. Some minerals let light pass straight through them; they are transparent. Other let light through, but its impossible to distinguish an object through them; they are translucent. Still others let no rays through at all; they are opaque.* STREAK *When a mineral is rubbed on a surface of unglazed porcelain, it leaves a powder trace. The colour of the powder may be different from that of the mineral itself, but it is always the same for that mineral. This trace is called a streak and is considered one of the mineral's characteristics. Idiochromatic minerals leaves a brightly coloured powder. Allochromatic minerals leave a white or pale powder.* HARDNESS *Hardness depends on the strength of the bonds uniting the atoms in a mineral. The Mohs scale assigns a value from 1 to 10 to a mineral to indicate its hardness, measured by its resistance to scratching.