Minerals

1. Minerals

2. Minerals: Building blocks of rocks To be considered a mineral, a substance must: be a naturally occurring solid be formed by inorganic processes have a crystalline structure (orderly molecular arrangement have a specific chemical composition

3. An element is a substance that cannot be broken down into simpler substances by chemical means Minerals are made up of one or more elements

4. Most abundant elements of the continental crust Common rock-forming minerals are mostly chemical compounds made up of these elements How do these elements combine to make minerals?

5. Atoms, molecules and ions Atomsare the smallest individual particle that retains the distinctive chemical properties of an element. Molecules are the smallest individual particle that retains the distinctive chemical properties of a chemical compound. Molecules consists of 2 or more atoms. Ions are atoms or molecules that have a net electrical charge. They attract oppositely-charged ions to form chemical compounds.

6. Crystalline Nature of Minerals Crystal: any substance whose atoms are arranged in a regularly repeating pattern Crystal growth is often interrupted due to: lack of space rapid cooling rate

7. Luster: Appearance of a mineral in reflected light • Metallic (ex: pyrite) Nonmetallic – glassy (hornblende)

8. Luster: Appearance of a mineral in reflected light • Nonmetallic- waxy (ex: chert) • Nonmetallic –dull (another chert)

9. Physical properties of minerals • Color • Generally an unreliable diagnostic property to use for mineral identification • Often highly variable for a given mineral due to slight changes in mineral chemistry

10. Quartz (SiO2) exhibits a variety of colors Figure 2.21

11. Physical properties of minerals • Streak • Color of a mineral in its powdered form • Helpful in distinguishing different forms of the same mineral • Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs scale of hardness

12. Streak – the color of a powdered mineral Figure 2.10

13. Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness

14. Physical properties of minerals • Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces • Described by resulting geometric shapes • Number of planes • Angles between adjacent planes

15. Common cleavage directions

16. Three examples of perfect cleavage – fluorite, halite, and calcite Copyright © 2006 Pearson Prentice Hall, Inc.

17. Classification of Minerals Rock-forming minerals • Common minerals that make up most of the rocks of Earth’s crust • Only a few dozen members • Composed mainly of the 8 elements that make up over 98% of the continental crust

18. Elemental abundances in continental crust Figure 2.15

19. Classification of Minerals • In most cases, minerals are grouped according to the major “building block” in the chemical structure. • Silicates (SiO44-) • Oxides (O22-) • Sulfides (S2-) • Sulfates (SO42- ) • Carbonates (CO32-) • Halides (Cl1- , F1- Br1- ) • Native Elements (single element)

20. Rock-forming Minerals – The Silicate Group • Most common mineral group due to large amounts of silicon and oxygen in Earth’s crust • Basic building block is the silicate ion: Four oxygen ions surrounding a much smaller silicon ion. • Polymerization: process by which silicate ions bond to form more complex ions, such as rings, chains, sheets or 3 dimensional frameworks.

21. Common Silicate minerals • Olivine Group • High temperature Fe-Mg silicate • Individual silicate linked together by iron and magnesium ions • Forms small, rounded crystals with no cleavage

22. Common Silicate minerals • Pyroxene Group • Single chain structures involving iron and magnesium • Two distinctive cleavages at nearly 90 degrees

23. Common Silicate Minerals • Amphibole Group • Double chain structures involving a variety of ions linking the silicate ion • Two perfect cleavages at non right angles Hornblende is the most common mineral in the amphibole group

24. Common Silicate Minerals • Mica Group • Sheet structures that result in one direction of perfect cleavage • Biotite is the common dark colored mica.

25. Common Silicate Minerals • Mica Group • Sheet structures that result in one direction of perfect cleavage • Muscovite is the common light colored mica.

26. Classification of Minerals • Common Silicate minerals • Feldspar Group • Most common mineral group • 3-dimensional framework that exhibits two directions of cleavage at 90 degrees • Orthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar) are the two most common members

27. Feldspar Minerals

28. Potassium feldspar - Orthoclase Copyright © 2006 Pearson Prentice Hall, Inc.

29. Calcium-rich plagioclase feldspar - labradorite

30. Quartz • Consists entirely of silicon and oxygen (SiO2). This is a material called silica. • Strong bonds in all directions – cleavage absent. • Naturally clear, but impurities cause colors.

31. Chert – Cryptocrystalline Quartz

32. Nonsilicate Rock-forming mineral groups • Carbonates- minerals found in exoskeletons of marine organisms. Calcite (calcium carbonate – CaCO3) is the most important carbonate mineral.

33. Nonsilicate Rock-forming mineral groups • Sulfates – minerals containing the sulfate ion • Gypsum (Calcium sulfate: CaSO4 – 2H2O. A product of rapid evaporation of ancient seas.