Chapter 3-2 How are Minerals Identified?

1. Chapter 3-2 How are Minerals Identified? Easy tests using mineral properties

2. How dense a mineral is depends on the mass of the atoms that make it up and how tightly packed together the atoms are. • Density=mass/volume Density

3. Many different minerals can be the same color. • The same mineral can be many different colors. • Differences in color can occur for several reasons: 1. impurities from added elements 2. contact with air and water 3. a defect in the crystal shape as it grows. COLOR

4. The color of a mineral in powdered form. • Nonmetallic minerals usually produce a white streak. • The same mineral will give the same streak color regardless of the sample color. Streak shows a mineral’s “TRUE” color. • Use an unglazed porcelain tile to draw the mineral across, pulling the powder from the sample. This is called a “streak plate” or “scratch plate”. Streak

5. The way a mineral reflects or absorbs light at its surface. • There are 2 main categories: metallic and nonmetallic • Metallic can be shiny or dull. • Nonmetallic has several categories. Some of the basic groups are: waxy silky pearly glassy earthy Luster

6. The way atoms are arranged and the strength of their bonds determine how a mineral breaks. • Minerals break where bonds are weak. • Smooth, flat surfaces = cleavage. (Ex. Mica, calcite) • Uneven surfaces, splinters, or curved surfaces = fracture. (Ex. Quartz) • When a mineral fractures it is where the atomic bonds are equal all around. Cleavage/Fracture

7. It is the resistance of a mineral to being scratched. • Minerals can only scratch other minerals that are softer than they are. • Hardness is determined by crystal structure. • The Mohs Hardness Scale goes from 1-10, 1 being the softest and 10 being the hardest. There are 10 specific minerals that used on this scale as comparisons. The softest is Talc and the hardest is a diamond. • In the field, ordinary items can be used to test minerals for their hardness. These items are: Fingernail—hardness of 2.5 or less Penny—3.5 Iron nail—4.5 Glass—5.5 Steel file—6.5 Hardness

8. Cubic—galena, pyrite, fluorite, diamond, garnet, magnetite • Hexagonal—quartz, aquamarine, emerald, hematite • Orthorhombic—calcite, aragonite, crystal sulfur, peridot, topaz • Monoclinic—selenite, uralite, biotite, gypsum, talc • Triclinic—ulexite, kyanite, labradorite, turquoise • Tetragonal—chalcopyrite • [Also, trigonal as seventh basic shape] Crystal Forms—6 basic shapes!

9. 3 special properties we will test: 1. Acid (HCl) test—minerals in the “carbonate” group will react with HCl to form CO2 bubbles (Ex. Calcite) 2. Fluorescence—some minerals glow under ultraviolet light (UV) and change colors. Different samples of the same mineral may not always glow though or they may glow a different color. Cool test, but not good to count on for identification. (Ex. Flourite) 3. Magnetic—some minerals will pull a magnet towards them because of their iron content. Hold a magnet loosely and move it towards the mineral to see if it creates even a small pull. (Ex. Magnetite) Special Properties