Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials

2. Unit 3: Topic 1.3 Mineral Properties Focus on . . . • identifying the three characteristics that all mineral properties depend on. • identifying and describing which mineral properties are most reliable when identifying minerals

3. Mineral Properties • Each and every mineral has certain mineral properties. The properties of each mineral depends on the following: • The type of elements present • The arrangement of atoms • The strength of bonding Text Reference: pages 40-44

4. Mineral Properties The following are a list of physical properties that each mineral may display:

5. 1) Specific Gravity • is the mass of a mineral compared to that of an equal volume of water. • To determine specific gravity you need to carry out the following three steps: • weigh the specimen in air and record the weight.

6. 1) Specific Gravity • is the mass of a mineral compared to that of an equal volume of water. • To determine specific gravity you need to carry out the following three steps: • 2) weigh the specimen submerged in water and record the weight.

7. 1) Specific Gravity • is the mass of a mineral compared to that of an equal volume of water. • To determine specific gravity you need to carry out the following three steps: • 3) calculate specific gravity (S.G.)using the following formula. • Specific Gravity = weight in air . weight in air - weightin water

8. 1) Specific Gravity = Density • Note: (In Reference to Core Lab #4) • Because pure water at 4 degrees Celsiushas a densityof 1 g/cm3, the specific gravity is equal to its density.Thus;Specific Gravity = Density. • To determine Density you need to: • Use a scale to measure the mass of the mineral sample. • Find the volume of the mineral sample. (water displacement) • Calculate density (which equals specific gravity). • Density = Mass (mineral) = Specific Gravity • Volume (mineral)

9. 1) Specific Gravity = Density Given: 1mL = 1cm3 = 1g, we know the weight of an equal volume of water in grams. We can then use the following formula to calculate Specific Gravity: Calculation S.G. = W (mineral) W (water) S.G. =

10. 2) Hardness • The resistance of a mineral to scratching. • Hardness is expressed in terms of Moh’s Hardness Scale which ranks relative hardness from 1 – 10. • You could use a rhyme to remember the hardness scale: • Tonight Gypsies Come From AfricaOn Quads To Catch Dinosaurs

11. 2) Hardness • The following objects can be used when trying to determine the hardness of different minerals. • If the object scratches the mineral then it is harder than the mineral.

12. Nail, hardness of 4.5 scratches a mineral. 2) Hardness • The following objects can be used when trying to determine the hardness of different minerals. • If the object scratches the mineral then it is harder than the mineral.

13. 2) Hardness • The following objects can be used when trying to determine the hardness of different minerals. • If the object scratches the mineral then it is harder than the mineral.

14. 3) Streak • The true color of the mineral in its powdered form. • To find the streak of a mineral, you perform a streak test. To do this you scratch a mineral across an unglazed porcelain tile and the powder streak left on the tile is the true color of the mineral.

15. 4) Cleavage • The tendency of some minerals to break along smooth, flat, parallel surfaces. • Cleavage directions are determined by atomic structure and strength of bonding.

16. 4) Cleavage • Cleavage directions are determined by atomic structure and strength of bonding. • The tendency of some minerals to break along smooth, flat, parallel surfaces. • Cleavage follows areas of weak bonding.

17. 4) Cleavage Plane Directions • Minerals show cleavage in many different directions, but most common are in planes of one, two, and three directions. • Cleavage in one direction (Basal Cleavage). Example: Mica displays this type of cleavage

18. 4) Cleavage Plane Directions • Cleavage in two directions.Example: Orthoclase feldspar displays this type of cleavage

19. 4) Cleavage Plane Directions • Cleavage in Three directions.Example: Halite displays this type of cleavage.

20. Example 1: What is the approximate hardness of an unknown mineral if it can be scratched by a copper penny but not by a fingernail? (A) < 2.5 (B) 2.5 - 3 (C) 4 - 4.5 (D) > 4.5 How many cleavage planes are visible in the mineral sample to the right? (A) 3 (B) 6 (C) 9 (D) 12

21. Example 2: A mineral sample with a mass of 75 g is placed in a graduated cylinder with 100 ml of water. The water level rises to 125 ml in the cylinder. What is the specific gravity of the mineral? (A) 0.33 (B) 3.0 50.0 (D) 75.0 Which mineral property is found by scraping a mineral across an unglazed porcelain tile? (A) double refraction (B) hardness (C) lustre (D) streak

22. Example 3: Question: Explain how Moh’s scale and items of known hardness are used to assist in the identification of an unknown mineral.

23. Example 3: Solutions . . . Moh’s scale ranks the hardness of a mineral from softest, value of one (1), to hardest, value of ten (10) and assigns a mineral to each hardness value. When identifying an unknown mineral, hardness is a property often used. Items of known hardness, such as a finger nail (2.5), copper penny (3.5), iron nail (4.5), steel knife (5.5), and glass (>6.0) can be used to identify the hardness of the mineral. These objects can be scratched across the mineral and if it scratches the mineral, the mineral is softer than the hardness value assigned to each object. The relative hardness can be narrowed down by scratching the mineral repeatedly by the different items of known hardness. Also, the hardness of a mineral can be determined by scratching the mineral with minerals of known hardness as identified by Moh’s hardness scale. If the mineral of known hardness fails to scratch the unknown mineral it is softer and the next hardest mineral on Moh’s scale can be used until a scratch is made in the unknown mineral.

24. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Questions: A pencil lead contains the mineral graphite which is composed of pure carbon and a diamond is also composed of pure carbon. How do their values for hardness compare on Moh’s Scale? Explain why the difference in hardness exists between diamond and graphite.

25. Solutions . . . Questions: Diamond (hardness of 10) has a higher value of hardness than graphite (hardness of 1) when comparing according to Moh’s hardness scale.. Diamond and graphite both contain carbon but have very different hardness because of the strength of bonding between carbon atoms and the arrangement of carbon atoms. The carbon atoms in diamond are arranged in a tetrahedral pattern and exhibit stronger bonding, whereas, the carbon atoms in graphite are arranged in a hexagonal layers with weak bonding between the layers. The high hardness of diamond on Moh’s hardness scale in comparison to graphite is mainly due to the stronger bonding and the more stable atomic structure.

26. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Which mineral exhibits the cleavage pattern shown? (A) calcite (B) feldspar (C) halite (D) mica

27. Solutions . . . Question: Which mineral exhibits the cleavage pattern shown? (A) calcite (B) feldspar (C) halite (D) mica

28. Summary . . . Overview of Points covered: • The properties of each mineral depends on the following:1) The type of elements present2) The arrangement of atoms3) The strength of bonding • Four most reliable mineral properties include:1) Specific Gravity • Hardness • Cleavage • Streak