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Minerals

Minerals. Review of Elements. An element is a substance that can not be broken down into other substances. 113 known elements (92 occur naturally) Periodic table of the elements Examples – Oxygen, hydrogen, gold…. Review of an Atom.

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Minerals

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  1. Minerals

  2. Review of Elements • An element is a substance that can not be broken down into other substances. • 113 known elements (92 occur naturally) • Periodic table of the elements • Examples – Oxygen, hydrogen, gold…

  3. Review of an Atom • An atom is the smallest possible particle of an element that still has all the properties.

  4. Review: Parts of an Atom • Electrons - (negative charge) Orbit around the nucleus in energy levels or shells • Protons - (positive charge) Located in nucleus • Neutrons – (neutral charge) Located in nucleus

  5. Atomic Number • Atomic number – represents the number of protons in an atom. • Neutral atoms have the same number of protons (+ charge) and electrons (- charge) • The atomic number is used to organize elements in the periodic table

  6. Examples of Atomic #, Atomic Mass Number

  7. Atomic Mass and Isotopes • Atomic mass – Total number of protons and neutrons (in nucleus) • Number of neutrons in an atom can change without affecting the atom. Elements containing different numbers of neutrons are called isotopes ex) Carbon 12 vs. Carbon14

  8. Forming Minerals • Some minerals can form from one element only. Example. Gold (Au) • Most minerals form when they one or more elements combine together. Example quartz (SiO2)

  9. How do elements bond together? • Elements bond together by sharing their electrons • known as covalent bonding • Electrons are given or taken away from one element to another • ionic bonding

  10. The Chemistry behind Table Salt • Chemical formula is NaCl • Composed of Sodium (Na) and Chloride (Cl) • Alone, sodium is soft, shiny, potentially explosive • Alone, chloride can be a toxic gas • Together they form harmless and essential table salt

  11. Most common minerals • Of the 92 naturally occurring elements, only 8 make up 98% of the Earth’s crust • Two very important elements • oxygen and silicon. • They combine covalently to form a 4-sided pyramid (known as a: tetrahedron) • Minerals containing silicon-oxygen tetrahedron are called silicates • (make up 1/3 of the minerals on Earth)

  12. Definition of a mineral • A naturally occurring solid that is crystalline (repeating arrangement of atoms) and has a specific chemical composition (chemical formula).

  13. Quartz crystals with Hematite "rosettes”

  14. http://www.exceptionalminerals.com/tucson2011-4.htm Tourmaline “watermelon” Orange Zircon

  15. More about minerals… • Minerals are the building blocks of rocks. • 4000 minerals have been identified • A mineral must: • Occur naturally • Have a chemical composition (formula) • Contain crystals (chrystalline)

  16. Mineraloids: • A mineral that does not have all three defining characteristics. • Example: Opal, Chrysocolla

  17. To identify an unknown mineral, you should: first determine its physical properties, then match the properties with the appropriate mineral, using a mineral identification key. How do geologists identify minerals?

  18. Physical Properties of Minerals • To identify a mineral, geologists will study various physical properties: • Colour • Streak • Lustre • Hardness • External crystal form • Cleavage • Fracture • Specific gravity • Other: Chemical tests

  19. 1) Color • not always reliable because color can be changed by the presence of impurities within the mineral, by the type of light used (natural, artificial), by weathering of the mineral’s surface. • Azurite is always blue, malachite is always green.

  20. 2) Streak • Color that is displayed when the mineral is rubbed across a streak plate (more reliable than just external color). • Streak color will not always be the same as the color of the mineral. • Galena streaks gray;Hematite streaks red.

  21. 3) Luster • how the mineral’s surface reflects light (shiny, glassy, silky, pearly, etc.) • Galena has a metallic luster

  22. 4) Hardness • The “scratchability” or hardness of a mineral. • For a true hardness test, the hardner mineral or substance must be able to make a groove or scratch on a smooth, fresh surface of a softer mineral. • Example…

  23. Example of hardness test: Quartz • Quartz can always scratch calcite

  24. Mohs’ hardness Scale • 10 minerals are designated as standards of hardness. • Softest mineral = talc • Hardness mineral = diamond • http://www.youtube.com/watch?v=7piTh8mH9zw

  25. Increasing hardness Mineral Hardness Hardness of Some Common Objects Talc 1 Gypsum 2 Human fingernail (2.5) Calcite 3 Copper penny (3.5) Fluorite 4 Apatite 5 Glass (5-6) Pocketknife blade (5-6) Orthoclase (potassium feldspar) 6 Steel file (6.5) Quartz 7 Topaz 8 Corundum 9 Diamond 10 Mohs Hardness Scale Increasing Hardness

  26. Hardness Test… • Geologists rely on common objects to test for hardness. • Fingernail usually has a hardness of about 2.5 • If you can scratch a mineral with your fingernail it has a hardness of less then 2.5. • A penny has a hardness between 3-4 • A knife blad or a steel nail generally has a hardness of slightly greater than 5. • Glass has a hardness of ~ 5.

  27. How to conduct a hardness test on a mineral: • Website: http://www.oum.ox.ac.uk/thezone/minerals/detect/hardness.htm • Video Clip http://www.youtube.com/watch?v=Pz0L6LwGswA

  28. Mohs’ Scale Activity • Complete activity sheet

  29. 5) Crystal Form • The set of faces that have a definite geometric relationship to one another.

  30. Examples ZIRCON GYPSUM QUARTZ RHODONITE

  31. 6) Cleavage • tendency to break consistently along distinct planes. • Example, halite always forms cubes

  32. 7) Fracture • When minerals don’t cleave, they fracture – break at random, forming jagged, irregular surfaces.

  33. 8) Specific Gravity • is a comparison of the weight of the mineral to the weight of an equal volume of water. • Example: • GOLD has a specific gravity of 19.3, which means that it weighs 19.3 times as much as an equal volume of water.

  34. Specific Gravity… • Specific gravity can be used to distinguish gold from pyrite (fools gold) which has a specific gravity of only ~4.

  35. 9) Other Tests: Smell and Taste • sulfur-containing minerals stink like rotten eggs • halite is salty tasting Sulfur Halite

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