definite chemical composition and

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1 MINERALS Building blocks of rocks Mineral: is a homogeneous substance that has a definite chemical composition and an orderly geometric arrangement of atoms. 1 Minerals: Naturally occurring Inorganic solid Ordered internal molecular structure Definite chemical composition 2 1

2 Nearly 4000 minerals have been identified on Earth. 3 Identification of Minerals Minerals can be only identified absolutely by X ray analysis and chemical tests. The x ray analysis determines the structure of the mineral and the chemical tests determine the composition of the mineral. Structure and composition are the defining marks of a mineral. 4 2

3 X ray analysis 5 Unfortunately, these tests require: expensive equipment, expert know how and often destroy the specimen. Fortunately, both structure and composition affect certain physical properties. It is through the proper use of these properties that minerals can reliably be identified. 6 3

4 The Physical Properties of Minerals Structure (Crystal Form) Hardness Cleavage Fracture Specific Gravity Color Streak Luster Tenacity 7 Crystal Form is the external shape produced by a minerals internal crystalline structure. This happens when a mineral grows (or solidifies) without interference or obstacle. 8 4

5 ISOMETRIC DIAMOND TETRAGONAL WULFENITE HEXAGONAL BERYL TRIGONAL QUARTZ variety - AMETHYST ORTHORHOMBIC TANZANITE MONOCLINIC GYPSUM TRICLINIC MONTEBRASITE AMORPHOUS AMBER 9 Hardness is a measure of a mineral's resistance to abrasion. is determined by the relative ease or difficulty with which one mineral can scratch another. Ui Using known mineral samples to test the hardness of an unknown is common practice. 10 5

6 Hardness With a systematic approach, you can use minerals of known hardness to dt determine the relative hardness of any other mineral. A mineral of a given hardness will scratch a mineral of a lower number. 11 You can use the following items to help estimate the hardness of a mineral: Finger Nail (H = 2.5) Penny (H = 3) Knife Blade (H = 5.5) 12 6

7 The Mohs Hardness Scale: Hardness number Mineral 1 Talc 2 Gypsum 3 Calcite 4 Fluorite 5 Apatite 6 Orthoclase 7 Quartz 8 Topaz 9 Corundum 10 Diamond 13 #1 Talc #5 Apatite #2 Gypsum #6 Orthoclase #3 Calcite #8 Topaz #9 Corundum MINERAL Hardness scale: 1 Talc 2 Gypsum 3 Calcite 4 Fluorite 5 Apatite 6 Orthoclase 7 Quartz 8 Topaz 9 Corundum 10 Diamond #4 Fluorite #7 Quartz #10 Diamond 14 7

8 Fracture and Cleavage If a mineral fractures, it breaks along rough edges. If it cleaves, then it breaks along smooth, flat surfaces. 15 Cleavage is the tendency of a mineral to break in certain preferred directions along smooth planes. 16 8

9 Cleavage 17 Fracture is a description of the way a mineral tends to break. It is different from cleavage. The broken surface is irregular. 18 9

10 The most common fracture type is: FRACTURE Smooth or rough curved break Conchoidal Fibrous or splintery break Splintery Rough surface with sharp edges Hackley Rough surface Uneven 19 Conchoidal Fracture (Quartz and Obsidian) When some minerals fracture, they appear to break along long curved surfaces (that looks like a shell) This type of fracture is known as conchoidal lfracture Quartz and the igneous rock Obsidian will demonstrate this type of fracture

11 Splintery Minerals such as asbestos break into long fibrous. 21 Specific Gravity Specific gravity is a measure of the density of a mineral. It is derived dfrom the density of the mineral ldivided id d by the density of water. At times it is such a useful property that it is the only way to distinguish some minerals without laboratory or optical techniques. Example: Gold can easily be distinguished from fool's gold, Pyrite" by specific gravity alone, although there are many other ways

12 Specific Gravity Minerals Specific gravity sulfur, graphite 1 2 gypsum, quartz, calcite 2 3 fluorite, beryl 3 4 corundum, most metal oxides, pyrite 4 6 native gold, platinum COLOUR Color is the first thing someone notices when they view a mineral. Color is also one of the big reasons that attract people to minerals. Generally speaking, color is not a good property to be used in the identification of minerals. Many minerals have different colors and some minerals' colors are identical to other minerals' colors. It is important to understand what causes color in minerals in order to understand this mineral property

13 EXAMPLES QUARTZ Clear quartz is white or cloudy (milky quartz). Purple (Amethyst), Pink (Rose Quartz), Gray or brown to black (Smoky Quartz) are also common. 25 QUARTZ 26 13

14 Smoky Quartz 27 QUARTZ : Purple (Amethyst) 28 14

15 AZURITE Color is azure, deep blue or pale blue if found in small crystals or crusts. 29 OLIVINE Color is a light near emerald green to the more common pale yellowish green; also found colorless, greenish brown to black

16 CALCIUM PLAGIOCLASE 31 SODIUM PLAGIOCLASE 32 16

17 POTASSIUM FELDSPAR 33 Streak Streak is the color of a powdered mineral. Streak can be different than color. This is usually determined by running the mineral across a piece of unglazed porcelain called a streak plate (or just unglazed white tile found at the hardware store)

18 THE MINERAL HEMATITE Example Streak THE MINERAL GALENA 35 Two minerals that have similar outward color may have different colors when powdered. Hematite's streak is blood red, Galena's streak is lead gray. Hematite (pictured above) is probably the most well known example of streak with its completely surprising streak color

19 Luster: is the appearance of light reflected from a minerals surface. Unique terms : Dull just a non reflective surface of any kind Earthy the look of dirt or dried mud Fibrous the look of fibers Greasy the look of grease Metallic the look of metals Pearly the look of a pearl (Ex. Sanbornite ) Silky the look of silk Waxy the look of wax 37 Luster Metallic Luster Waxy Luster 38 19

20 Tenacity Tenacity refers to a mineral s resistance to breaking, bending, or otherwise being deformed. A mineral may be brittle, easily broken or crushed to powder; 39 malleable, easily hammered into thin sheets (such as copper or gold); sectile, easily cut with a knife; flexible, easily bent without breaking and then staying bent; or elastic, bending but resuming its original shape once pressure is released

21 Tenacity is particularly useful in telling some of the metallic minerals apart. Gold is malleable, pyrite (and most other look a likes) is not. Gold is also sectile and in thin sheets flexible. Galena is brittle, while platinum is malleable and sectile. 41 Minerals are grouped as: Silicate Nonsilicate 42 21

22 Silicates: Most important mineral group Comprise most of the rock forming minerals Very abundant due to large amounts of silicon and oxygen in Earth s crust The simple ions of Silicon and Oxygen tend to bond together to form a complex ion Silicate Anion (SiO4) 4 The Silicate Anion bond with other elements and form minerals 43 Quartz (SiO 2 ) Common Silicate minerals Feldspar Group (Orthoclase: potassium feldspar and Plagioclase :sodiumand calciumfeldspar) Mica Group (Biotite is the common dark colored mica mineral (Muscovite is the common light colored mica mineral) Amphibole Group (Hornblende is the most common) Pyroxene Group (Augite is the most common) Olivine (Forms small, rounded crystals with no cleavage) Clay minerals (Kaolinite, Illite, Montmorillonite, etc.) 44 22

23 Nonsilicate minerals Several major groups exist including: Group Native Elements: Carbonates Oxides Sulfides Sulfates Mineral Gold, Copper, Diamond, Sulfur, Graphite Calcite, Dolomite Hematite, Magnetite, Chromite Galena, Pyrite, Chalcopyrite Gypsum, Anhydrite 45 Carbonates Carbonates are among the most abundant nonsilicate minerals in the Earth's crust. The sedimentary rock LIMESTONE is composed of carbonate minerals The basic building block of carbonates is the carbonate ion (CO 3 )

24 Carbonates The carbonate ion (CO 2 3 ) can bond with a variety of other ions to produce the carbonate minerals. The bonding with calcium to form the mineral calcite (CaCO 3 ). produces one of the most abundant of the non silicate minerals. All carbonates have the property of dissolving easily in acidic water. 47 These carbonate minerals form by Precipitation from marine or freshwater Secretion by organisms as shells or skeletons 48 24

25 THE CLAY MINERAL GROUP Clay minerals are the product of the chemical weathering of silicate minerals, especially the feldspars. The clay minerals are a part of a general but important group within the phyllosilicates that contain large percentages of water trapped between the silicate sheets. 49 SOME PROPERTIES of THE CLAY MINERALS They can absorb water or lose water from simple humidity changes. When mixed with limited amounts of water, clays become plastic and are able to be molded and formed in ways that most people are familiar with as children's clay. When water is absorbed, clays will often expand as the water fills the spaces between the stacked silicate layers

26 Due to the absorption of water, the specific gravity of clays is highly variable and is lowered with increased water content. The hardness of clays is difficult to determine due to the microscopic nature of the crystals, but actual hardness is usually between 2 3 and many clays give a hardness of 1 in field tests. Clays arerarelyrarely found separately and areusually mixed not only with other clays but with microscopic crystals of carbonates, feldspars, micas and quartz. 51 Clay minerals are divided into four major groups: The Kaolinite Group The Smectite Group (Montmorillonite) The Illite (or The Clay mica) Group The Chlorite Group 52 26

27 Ore minerals Some of the most important ore minerals and the metals extracted from them Metal Minerals Iron Copper Aluminum Gold Silver Lead Zinc Hematite, Magnetite Chalcopyrite, Native copper Bauxite Native gold, Pyrite Native silver Galena Sphalerite 53 Rock Stability Minerals which form at: high temperatures and pressures are least stable, and weather most quickly lower temperatures and pressures are most stable

28 Texture of Rocks SMALL CRYSTALS COOLED QUICKLY (because of the reduced time for atoms to attain minimum energy configuration) BIG CRYSTALS COOLED SLOWLY Cooling may be so rapid, as in a volcanic eruption, that no crystalline structure develops before solidification: and an amorphous material such as obsidian (volcanic glass) is formed. 55 Bowens reaction series Each mineral is more stable than the one above it on the list