What is a Mineral?

1. What is a Mineral?

2. What is a mineral? • Elements which can be described in chemical terms or compounds composed of two or more elements and found occurring naturally in the Earth are termed minerals.

3. Some general facts: Over 2,000 minerals have been identified. Elements combine to form minerals. Some minerals are “native elements.” That means they are made of only one element, like gold, copper, and sulfur.

4. Native Elements Gold Sulfur

5. How do we identify minerals? • Physical Properties • Chemical Properties

6. How do we identify minerals? Physical • Crystal Form • Crystal form indicates the internal molecular arrangement of the mineral • There are six forms • Isometric • Hexagonal • Tetragonal • Orthorhombic • Monoclinic • Triclinic

7. How do we identify minerals? Physical • Moh’s Scale of Hardness • Hardness • its ability to resist scratching

8. How do we identify minerals? Physical • Specific Gravity • Relative weight of a mineral when compared to the specific gravity of that mineral. The specific gravity of water is 1.0.

9. How do we identify minerals? Physical • Cleavage • The way in which some minerals will split or cleave precisely along planes related to the internal molecular structure.

10. Where does cleavage occur? • It occurs along certain planes of weakness that exist in some minerals because of their atomic structure. • Some minerals have cleavage in one, two, three, or more directions.

11. Fluorite

12. How do we identify minerals? Physical • Fracture • If a mineral breaks unevenly along rough or curved surfaces instead of cleavage, this is called fracture.

13. How do we identify minerals? Physical • Color • The coloration of a mineral may be due to many factors, including chemical composition, trace elements, impurities, oxidation, and tarnishing.

14. These 3 are all colors of quartz.

15. How is color useful for identifying minerals? • The color of a mineral is the first thing that people notice. • But it can also be the least useful in identifying a mineral. • Most minerals occur in more than one color, due to impurities or chemical differences. For example, fluorite can be clear, white, yellow, blue, purple, or green. Quartz also can be different colors.

16. For which minerals is color a useful tool for identification? • For some minerals, the color is due to the major elements and can be a characteristic way to identify a mineral. For example, malachite is always green, and azurite is always blue.

17. How do we identify minerals? Physical • Streak • When a mineral is rubbed against a a piece of unglazed porcelain tile, a steak of power will result. The streak may differ from the color of the mineral and them become a valuable clue to its identification.

18. How do we identify minerals? Physical • Example: Hematite, for example always gives a reddish brown streak no matter what type of luster it displays.

19. How do we identify minerals? Physical • Luster • The surface of a mineral as it absorbs, reflects, or refracts light is termed luster • Metallic- Minerals with metallic luster look like metal, with a silvery appearance, or the flat metallic look of steel. • Non Metallic may look pearly, greasy, or glassy

20. Metallic Luster Pyrite Galena

21. What is Non-metallic Luster? Quartz • Some Non-metallic luster may look: • Pearly • Greasy • Glassy

22. How do we identify minerals? Physical • Other Properties • Some minerals can be identified by other unique characteristics. • Radioactivity (with a Geiger Counter) • Magnetism (with a magnet) • Fluorescence (Ultraviolet light)

23. There are 9 steps to mineral identification • Step 1: Determine the crystal form • Step 2: Determine the hardness • Step 3: Look up the specific gravity • Step 4. Determine whether your mineral had cleavage (breakage). • Step 5: Look at the fracture • Step 6: Determine the color • Step 7: Determine the streak color • Step 8: Determine the luster • Step 9: Look at other properties • Name that mineral!

24. Mineral Identification

25. Let’s try to identify a few of our own…