What is a Mineral? A mineral must occur naturally in the Earth’s crust. It cannot be a manufactured or manmade item. A mineral must be inorganic rather than organic. Organic materials are formed from living things. A mineral is always a solid. Minerals cannot be liquids or gases. A mineral has a definite chemical composition. Minerals may be made of a single element. Some minerals are formed by compounds, or combinations of two or more elements. A mineral’s atoms are arranged in a definite pattern. This repeating patter is called a crystal.

Tuesday, June 07, 2016 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 we will use to identify minerals: –1. color –2. crystals (the shape of) –3. hardness –4. streak –5. cleavage and fracture –6. luster

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

In addition, a mineral can come in more than one color. For example, the mineral corundum can occur in several different colors 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 color a mineral leaves behind when it is rubbed on a hard surface (usually a streak plate) Often the color a mineral leaves behind is different from the color 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. Luster Luster – the way a mineral reflects light The "shininess," or luster 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 Luster - the mineral reflects light like a polished piece of metal.

2. Dull Luster - the mineral scatters the light and will not appear shiny at all.

Other Distinguishing Factors Density Magnetism Reactivity Senses