1. 1 How can we differentiate the rock forming minerals quartz (SiO 2 ) from calcite (CaCO 3 )? Professor Howard Lee McLean Department of Chemistry Rose-Hulman Institute of Technology

2. 2 Web resources

3. 3 Vocabulary fracture cleavage isometric prismatic onchodial crystal habit

4. 4 Defintions ___ the shape in which a mineral’s individual crystals or aggregates of crystals growth (NaCl on a string; body salt) ___ geometric pattern generated because of the crystal’s tendency to break along flat planar surfaces ___ nongeometric pattern generated because of breakage along irregular surfaces ___ wavy breakage

5. 5 Crystal habit – covalent and ionic bonds control neighbors garnet (garnet schist) isometricwell formed or rounded conchoidal fracture or irregular fracture quartz check cover of Mineralogy book single to six-sided primatic to massive crystals conchodial fracture to nondetectable cleavage tenacity – brittle

6. 6 How prominent is the cleavage? Mineral cleavage (vs. rock cleavage) one directionmuscovite.biotite two directions (|)K-felspar.Ca-feldspar two directionsamphipole.pyroxene three directions (|)halite three directionscalcite four directionsfluorite six directionssphalerite

7. 7 Cleavage is the tendency of a crystal to break along a flat planar surface or zone of weakness. decreases with bond strength bond strength is low, cleavage is good -- mica bond strength is high, cleavage is poor -- quartz is classified according to primary attributes: number of planes and pattern of cleavage quality of surface and ease of cleaving

8. 8 Hardness and cleavage Hamblin; Howard, EPG, 2007.

9. 9 Cleavage reflects light like a mirror results from planes of weakness within the crystal structure along which the crystal breaks. in contrast, crystal faces reflect the geometry of the atomic structure (crystal habit) cleavage planes reflect light in a particular direction; whereas fracture surfaces reflect light in all directions

10. 10 Electrostatic attraction between layers and not covalent / ionic bonding

11. 11 Flaky minerals and their zone of weakness between layers What mica exhibits one dimensional cleavage along zone of bonding weakness? basal cleavage

12. 12 How many cleavage planes? Identify specimens in TRC What are THREE positive tests and one negative test used to id?

13. 13 Very common rock forming minerals (like the classics) elongated rectangular cleavage

14. 14 What type of cleavage is observed? What are the three common rock forming minerals illustrated below?

15. 15 Another classic example elongated parallelogram cleavage

16. 16 How cleavage surfaces and what are the geometries (degrees)?

17. 17 Halite (sylvite) type cleavage and common optical property cubic cleavage This mineral also exhibits a cubic crystal habit. This may be confusing. Transparent to translucent optical property.

18. 18 Cleavage and interesting optical property of materials rhombohedral cleavage

19. 19 Cleavage apparent (H ~4) octahedral cleavage

20. 20 Cleavage (not in The Rx Colln) dodecahedral cleavage

21. 21 Cleavage and minerals micas (biotite, muscovite, vermiculite) feldspars (K to Na to Ca-feldspar) amphiboles (horneblende; cl ~56 0 and 124 0 ) pyroxenes (cl ~ 90 0 ) carbonates (calcite, malachite) sulfides (pyrite, galena, chalcopyrite)

22. 22 Twinning NAGT

23. 23 Lamellae Notice the fracture surface Notice the cleavage surfaces What angle? NAGT slide

24. 24 Less pronounced talc one perfect and flaky type texture (slippery feel) foliated and very small aggregates gypsum one perfect, splitting to distinctive slab usually two well pronounced, slabs or sheets granular, earth and finely crystalline masses, or even tabular crystals magnetite occasional octahedral isometric crystal habit conchodial or irregular fracture hematite no fracture or uneven, splintery fracture