1. Minerals II: Physical Properties and Crystal Forms From: http://webmineral.com/data/Rhodochrosite.shtml

2. The Physical Properties of Minerals Color Luster Streak Hardness Cleavage External Crystal Form

3. The Physical Properties of Minerals (cont.) Fracture Specific Gravity Special Properties Other Properties Chemical composion

4. Important Physical Properties II Color - with color or without (glassy) Although an obvious feature, it is often unreliable to use to determine the type of mineral. –Not original: Color arises due to electronic transitions, often of trace constituents. For example, quartz is found in a variety of colors. Color of a mineral may be quite diagnostic for the trace element and coordination number of its bonding environment.Quartz (yallow,pink or white) False color :which reflect different color labrodorite

5. Hope Diamond: 44.5 carats http://www.nmnh.si.edu/minsci/hope.htm

6. Important Physical Properties I Luster - - This property describes the appearance of reflected light from the mineral's surface. Metallic: Gold(Au),Cupper(Cu),silver(Ag),Pyrite (FeS 2 ). Nonmetallic minerals are described using the following terms: vitreous( زجاجي): Quartz(SiO 2 ), Calcite(CaCO 3 ),Halite (NaCl) pearly :(لؤلؤي) Mica, Muscovite KAl 2 (AlSi 3 ) O 10 (OH,F) 2. silky (حريري ) Fibrous Gypsum, resino (صمغي) Sulfur S, and earthy Kaolin (ترابي ),Diamond C :Diamond

7. Important Physical Properties III Streak - The color of a mineral in its powdered form, obtained by rubbing the mineral against an unglazed porcelain plate. –Streak is usually less variable than color. –Useful for distinguishing between minerals with metallic luster. –Talc is in different color but its streak is white

8. Important Physical Properties V Hardness - This is the resistance of the mineral to abrasion or scratching. This property doesn't vary greatly from sample to sample of the same mineral, and thus is highly diagnostic. It also is a direct reflection of the bonding type and internal atomic arrangement. A value is obtained by comparing the mineral to a standard scale devised by Moh, which is comprised of 10 minerals ranging in hardness from talc (softest) to diamond (hardest).

9. Mohs’ Hardness Scale

10. Fingernail Hardness (2.5) Scratches Gypsum (2)

11. Density and Specific Gravity Density - Defined as the mass divided by the volume and normally designated by the Greek letter, rho,  –  mass/volume; geologists often use g/cm 3 as the unit of choice. Specific Gravity - Ratio of the mass of a substance to the mass of an equal volume of water. Note that  water = 1 g cm -3. S.G. is unitless. Examples - quartz (SiO 2 ) has a S.G. of 2.65 while galena (PbS) has a S.G. of 7.5 and gold (Au) has a S.G. of 19.3.

12. Important Physical Properties VI Cleavage - Orientation and number of planes of weakness within a mineral. Directly reflects the orientation of weak bonds within the crystal structure. This feature is also highly diagnostic, Mica, muscovite and Biotite broken in one direction. Fracture - This describes how a mineral breaks if it is not along well defined planes. In minerals with low symmetry and highly interconnected atomic networks, irregular fracture is common. Conchoidal Fracture in Glass, chert – planey, Pyrite not planey, Gypsum fibrouse

13. Conchoidal Fracture in Glass

14. Planer Cleavage in Mica

15. Weak Bonding Yields Planer Cleavage

16. Amphibole Cleavage ~120/60°

17. Rhombohedral Cleavage in Calcite

18. Special and Other Properties Striations - Commonly found on plagioclase feldspar. Straight, parallel lines on one or more of the cleavage planes caused by mineral twinning. Magnetism - Property of a substance such that it will spontaneous orient itself within a magnetic field. Magnetite (Fe 3 O 4 ) has this property and it can be used to distinguish it from other non- magnetite iron oxides, such as hematite (Fe 2 O 3 ). Double Refraction - Seen in calcite crystals. Light is split or refracted into two components giving rise to two distinct images.

19. Plagioclase striations

20. Calcite Double Refraction

21. Color and Density Two broad categories are ferromagnesian and nonferromagnesian silicates, which simply means iron and magnesian bearing or not. The presence or absence of Fe and Mg strongly affects the external appearance (color) and density of the minerals. Ferromagnesian silicates - dark color, density range from 3.2 - 3.6 g/cc –Olivine - high Temp., low silica rocks; comprises over 50% of upper mantle –Pyroxenes - high Temp., low silica rocks –Amphiboles - esp. hornblende; moderate Temp., higher silica rocks –Mica - esp. biotite; moderate Temp., higher silica rocks –Garnet - common metamorphic mineral Nonferromagnesian silicates - light color, density close to 2.7 g/cc –Mica - exp. muscovite; moderate Temp, higher silica rocks –Feldspars - plagioclase and orthoclase; most common mineral in crust; form over a wide range of temperatures and melt compositions –Quartz - low Temp., high silica rocks; extremely stable at surface, hence it tends to be a major component in sedimentary rocks. –Clay - esp. kaolinite; different types found in different soil

22. Crustal Minerals

23. From http://www.geo.wvu.edu/~lang/Geol284/Min8IgFels More Zoning

24. Zoning in Plagioclase Feldspar Ca-rich core Na-rich rim

25. Important Physical Properties IV Crystal form or habit - The external morphology of crystals generally reflect the internal arrangement of their constituent atoms. This can be obscured, however, if the mineral crystallized in an environment that did not allow it to grow without significant interaction with other crystals (even of the same mineral).

26. Chrysotile Asbestos Belongs to the Serpentine mineral family - hydrated ferromagnesian silicate.

27. Crystal Forms: Quartz

28. Feldspar

29. Intergrown cubic crystals of fluorite

30. Quartz Interfacial Angles Perfectly Proportioned Crystals Misshapen Crystals Steno’s Law (1669): Crystal face internal angles remain constant!

31. Macroscopic Forms and Microscopic Blocks Cubes Rhombs Macroscopic Crystal Forms

32. Unit Cells and Crystal Structure Cubic unit cell: smallest repeatable unit

33. Polymorphism and polymorphs Substances having the same chemical composition but different crystal structures. –e.g. diamond and graphite Both minerals are composed of pure carbon, but diamond is the high pressure polymorph of graphite. This gives rise to extremely different physical properties.

34. Polymorphism Graphite & CalciteNatural Octahedral Diamond 3 mm From: http://www.phy.mtu.edu/~jaszczak/diamond.html

35. Diamond vs. Graphite Crystal Structures From: http://www.molecules.org/elements.html#diamond Hardness: 10Hardness: 1-2

36. X-ray diffraction: Laue photographic method

37. Bragg Relationship From: http://www.geology.wisc.edu/~g203/xray.htm

38. Laue X-ray photograph of Vesuvianite From: http://www.geology.fau.edu/course_info/fall02/gly4200/X-RAY.htm

39. Vesuvianite: Contact Metamorphic Mineral Formula: Ca 10 (Mg,Fe) 2 Al 4 Si 9 O 34 (OH) 4 System:Tetragonal Hardness: 61⁄2 http://www.mindat.org/min-4223.html