Unit 2: Rocks and Minerals

1. Unit 2: Rocks and Minerals Minerals: The Building Blocks of Rocks

2. Why study minerals? • The lithosphere is composed of naturally formed material made of one or more minerals called rock. Before we study the different types of rocks that make up the lithosphere, we must first look closely at the minerals that make up these rocks.

3. What is a mineral? A mineral is any substance that fits the following criteria: • Natural - not man-made • Inorganic - not alive, not from something alive, not once alive • Solid - not liquid, not gas • Definite chemical composition (ex/halite=NaCl; galena=PbS) • Orderly atomic arrangement (crystalline)

4. What are minerals made of? • To better understand the differences between minerals we need to discuss the elements that make up minerals. • An element is a substance that cannot be broken down by ordinary chemical means. A mineral can be composed of single elements or compounds of two or more elements. Elements themselves are composed of even smaller particles called atoms.

5. What is an atom? • An atom is the smallest part of an element that still contains all of the properties of that element. • In the nucleus of an atom we find protons and neutrons, while electrons can be found in a cloud surrounding the nucleus. Atomic number- the number of protons in an atom Atomic mass- the total mass of the particles in the atom’s nucleus (protons + neutrons)

6. Minerals made from more than one element are composed of compounds of elements. That is, minerals have a definite chemical composition and atomic structure due to the chemical bonding of the elements. Minerals made from only one element are said to be monomineralic. Minerals made from two or more elements are said to be polymineralic. Compounds vs. Mixtures Compounds- two or more elements combined chemically. Compounds can have properties different from those of the elements from which it is made. Mixture- two or more substances blended together, but not chemically combined. How do elements combine to form minerals?

7. Most elements are found in nature in compound form. A few elements are found as pure native elements. These are classified as minerals. Gold Silver Iron Copper Sulfur Diamond (carbon) Native Elements

8. What are the two main types of chemical bonds? • Ionic bonds form between metals that lose electrons to form positive ions, and nonmetals that gain electrons to form negative ions.

9. What are the two main types of chemical bonds? • Covalent bonds tend to form between nonmetals. In covalent bonding atoms share electrons.

10. What is the importance of chemical composition and bonding in the study of minerals? • All observable mineral characteristics (color, streak, luster, chemical reactions) result directly from the elements and/or compounds from which they are made. • The internal arrangement of atoms will determine the shape, hardness, density and cleavage of a mineral.

11. The internal arrangement of atoms determines what a substance is like. Diamonds and graphite are both made of carbon. In a diamond, the carbon atoms have stronger bonds. **The picture above shows how the arrangement of carbon atoms differs for diamond (left) and carbon (right).

12. How do minerals form? • Magma is a “soup” of molten (melted) minerals underground. Above ground, it is called lava. As magma cools, some minerals crystallize (solidify) before others. This allows different minerals to form separately from each other.

13. Some Common elements on Earth… • The eight most abundant elements in Earth’s crust are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. The majority of minerals are composed of these elements. See ESRT page 11.

14. What are the different categories of minerals? • Silicates: make up over 90% of Earth’s crust. Example- quartz • Carbonates: contain CaCO3. Examples- calcite, dolomite • Oxides: metal combines with oxygen. Examples- hematite, magnetite • Sulfides: metal combines with sulfur. Example- pyrite

15. More on Silicates… • Silicate minerals make up over 90% of Earth’s crust and are built around the silica tetrahedron (see diagram). • In some silicates the tetrahedra are joined in chains. • In others the tetrahedra are arranged into sheets, or three-dimensional networks.

16. How do we use minerals? • Chemical composition and physical properties determine how humans use minerals. • The properties of rocks determine how they are used and also influence land usage by humans. • Renewable resource- a resource that can be replaced in nature at a rate close to its rate of use (oxygen, trees, food, solar energy). • Nonrenewable resource- a resource that is used up faster than it can be replaced in nature (iron, aluminum, sand, coal, oil, natural gas, uranium).

17. How do we Identify Minerals? We use the properties of Minerals to help identify them.

18. Regents alert !!! • All the properties of a mineral are determined by their Internal Arrangement of Atoms.

19. Properties of Minerals: • Color • Hardness • Luster • Streak • Cleavage • Acid Test • Density

20. Color • Minerals come in many colors. • Sometimes even one mineral may be found in different colors. • That is why color alone is not enough to identify a mineral.

21. Hardness • Some minerals can scratch other minerals. The minerals that do the scratching are said to be harder than those that get scratched.

22. Hardness • http://www.amfed.org/t_mohs.htm • Moh’s scale of hardness rates mineral hardness on a scale of 1(soft) to 10(hardest).

23. Luster • The appearance of light reflected from a mineral’s surface. • Metallic • Glassy • Dull

24. Streak • The color of the powder that is left when a mineral is scratched across a streak plate. • The streak of a mineral is often a different color than the mineral itself. • Some minerals leave no streak.

25. Cleavage: • Some minerals tend to break along one or more predictable surfaces. • If you break a Kit Kat bar, it has cleavage.

26. Fracture: • Some minerals break in an unpredictable random fashion called fracture. • This Milky Way bar would fracture if you broke it.

27. Acid Test: • A few minerals will react with Hydrochloric acid. • When a drop of acid is placed on the mineral it will give off bubbles of Carbon Dioxide.

28. Density • Of course calculating the density of a mineral sample is a very good way to help identify the mineral.

29. Time to go out there and identify some minerals!!