Saturday, June 04, 2016 The Earth’s Crust Mineral Identification

Mineral Identification What differences can you see between these minerals that could help identify them? What properties could be used to identify minerals?

There are six main characteristics that can be used to identify minerals: –1. colour –2. crystals (the shape of) –3. hardness –4. streak –5. cleavage and fracture –6. luster

1. Colour Colour - It's pretty easy to tell the colour of a mineral and it can give a clue to the identity of the mineral. However, colour alone cannot identify a mineral. For example, pyrite (fools gold) and gold are both the same colour.

In addition, not all minerals are the same colour all the time. For example, the mineral corundum can occur in several different colours due to impurities. Corundum is better known as amethyst (purple), emerald (green), topaz (yellow), and ruby (red). In its pure form, corundum is white.

2. Crystals Crystal shape – Minerals sometimes occur as crystals. A crystal occurs naturally and has straight edges, flat sides, and regular angles. Each mineral forms a specific shape of crystal so it can be used for identification purposes.

3. Hardness Hardness – the hardness of a mineral can be measured and compared to other minerals using the Moh’s Hardness Scale.Hardness Scale The scale goes from one (the softest) to 10 (the hardest) and ranks minerals on their “scratchability” Mineral Mineral Hardness Hardness of Common Items talc1 (softest)Soft pencil point (1.5) gypsum2Fingernail (2.5) calcite3Copper penny (3.5) fluorite4Iron nail (4.5) apatite5Glass (5.5) feldspar6Steel file (6.5) quartz7Streak plate (7) topaz8Sandpaper (7.5) corundum9Emery paper (9.0) diamond10 (hardest)

4. Streak Streak – the colour a mineral leaves behind when it is rubbed on a hard surface (usually a streak plate) Often the colour a mineral leaves behind is different from the colour of the mineral.

5. Cleavage and Fracture Cleavage and Fracture – Describes how a mineral breaks apart

The way a mineral breaks apart can be a clue to its identity. If it breaks along smooth, flat surfaces, or planes, it is said to have cleavage. e.g. calcite or mica - Mica can be pulled apart into thin, flat, sheets and Halite forms flat edges when broken.

If it breaks with rough or jagged edges, it is said to have fracture. E.g. obsidian Obsidian fractures when broken apart leaving rough, jagged edges.

6. Lustre Lustre – the ability of a mineral to reflect light 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 including: 1. Metallic Lustre - the mineral reflects light like a polished piece of metal.

2. Vitreous Lustre (Glassy) - the mineral reflects light like a piece of glass when it is tilted from side to side.

3. Pearly Lustre- the mineral reflects light like a pearl.

4. Dull Lustre - the mineral scatters the light and will not appear shiny at all.