Chapter 10

 In this chapter, you will learn ◦ How minerals, rocks, and soils form and continue to change in a cycle. ◦ How soil types and crops vary across Canada. ◦ How human activity affects our environment positively and negatively.

 What is a rock?  Rock is made up of one or more minerals.  Minerals are pure, naturally occurring, non- living solid materials.  Minerals are quite rare. Only a few, such as quartz and mica, are common, found throughout Earth’s crust.

 A mineral can be an element (a pure substance) or a compound (two or more substances).  Quartz, for example, consists of the elements silicon and oxygen. No other mineral has these elements in the same arrangement and proportion.  Sulfur, copper, gold, and diamond, on the other hand, are made up of a single element.

 How can you tell minerals apart?  There are over 3,000 minerals. As a result, several properties are needed in order to correctly identify each one.  There are important clues when it comes to differentiating (telling the difference between) the properties of minerals.

 There are six (6) clues that we use to identify minerals: 1.Hardness (Mohs Hardness Scale) 2.Shape 3.Lustre 4.Colour 5.Streak 6.Cleavage and Fracture

 The Mohs Hardness Scale is a useful tool for mineral identification.  The scale lists ten (10) minerals with a “hardness” value from 1 (softest) to 10 (hardest).  A substance’s “scratchability” can be used for mineral identification. Softer minerals will scratch easily, as the harder the mineral (ex: diamonds), the more difficult it is to scratch it.

Friedrich Mohs ( )

 Minerals sometimes occur as crystals.  A crystal occurs naturally and has straight edges, flat sides, and regular angles.  All of the minerals in Earth’s crust can be grouped according to six (6) different crystal shapes.

 The “shininess”, or lustre, of a mineral depends on how light is reflected from its surface.  The surface of a mineral can reflect light in many different ways.  Some minerals (ex: gold) appear shiny. Others (ex: talc) can appear dull.  Most dull minerals are non-metals.

 Colour is one of the more attractive properties of minerals.  There are times, however, when colour alone cannot identify a mineral.  To complicate things even further, not all minerals are the same colour all of the time.

 Corundum ◦ The mineral corundum (made of aluminum and oxygen) is white when pure. ◦ When it contains iron and/or titanium, it is blue (and we call it a sapphire). ◦ When it contains chromium, it is red (and we call it a ruby). ◦ Oriental emerald (green), amethyst (purple), and topaz (yellow) are other coloured varieties of corundum.

 When a mineral is rubbed across a piece of unglazed porcelain tile, it leaves a streak.  A streak is the colour of the powdered form of the mineral.  Minerals with a greater hardness than the porcelain tile (hardness value of 7) will not leave a streak.

 Look-alike minerals, such as gold and pyrite, can be distinguished using a streak test.  When rubbed across a porcelain tile, gold leaves a yellow streak.  Pyrite, however, has a greenish-black or brown-black streak.

 The way a mineral breaks apart can be a clue to its identity.  If a mineral breaks along smooth, flat surfaces, it is said to have cleavage.  Minerals that break with rough or jagged edges have fracture.