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Matter and Minerals.

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Presentation on theme: "Matter and Minerals."— Presentation transcript:

1 Matter and Minerals

2 Minerals: Building blocks of rocks
Naturally occurring Solid Inorganic Definite chemical composition Crystal structure due to internal arrangement of atoms

3 General Facts about Minerals
Between 2 - 3,000 have been identified A few are “native elements” -- made of only one element, such as sulfur, gold. copper, and graphite (carbon) Most are compounds, especially the silicate group (Si, O). Other important groups are oxides, carbonates, and sulfides.

4 Less than a dozen are common in most rocks
Quartz Feldspar (group) Muscovite (white mica) Biotite (black mica) Calcite Pyroxene Olivine Amphibole (group) Magnetite, limonite, and other iron oxides Pyrite

5 How do we identify minerals?
Physical properties: Color Luster Hardness Crystal shape Cleavage Specific gravity Other

6 Physical Properties of Minerals
Color: Most obvious, but often misleading Different colors may result from impurities Example: Quartz

7 A mineral can be many different colors. Below is Mica.

8 Many minerals can be the same color. Below are gold colored minerals
Many minerals can be the same color. Below are gold colored minerals. Which one is gold?

9 Physical Properties of Minerals
Color: Streak – color of a mineral in powdered form (used for metallic minerals) Obtained by scratching a mineral on a piece of unglazed porcelain. Example: Hematite

10 Gold When gold is run across a streak plate it makes a yellowish-gold color.

11 Pyrite or “Fool’s Gold”
When pyrite is run across a streak plate, it has a black or dark green streak. Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.

12 Hematite Hematite’s color is grey, but its streak is red.
Hema means blood. The mineral was named hematite because it looked like it was bleeding when it was taken across a streak plate.

13 Physical Properties of Minerals
Luster: How a mineral surface reflects light Two major types: Metallic luster Non-metallic luster Metallic example: Galena Non-metallic example: Orthoclase

14 Pyrite has metallic luster

15 Quartz has vitreous luster

16 Physical Properties of Minerals
Hardness: How easy it is to scratch a mineral Mohs Scale of Hardness relative scale consists of 10 minerals, ranked 1 (softest) to 10 (hardest)

17 Mohs Scale of Hardness Hardest (10) – Diamond Softest (1) – Talc
Common objects: - Fingernail (2.5) - Copper coin (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5)

18 Gypsum is soft, it can be scratched by a fingernail.

19 Calcite is soft, but a little harder because it cannot be scratched by a fingernail, but it can be scratched by a coin

20 Fluorite is harder. It can be scratched by a nail, but not a coin or fingernail.

21 Diamond is the hardest mineral, so it scratches every mineral.

22 Physical Properties of Minerals
Crystal shape (or form): external expression of a mineral’s internal atomic structure planar surfaces are called crystal faces angles between crystal faces are constant for any particular mineral Quartz Pyrite

23 Physical Properties of Minerals
Cleavage vs. Fracture: The way a mineral breaks Cleavage: tendency of a mineral to break along planes of weakness Minerals that do not exhibit cleavage are said to fracture Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.

24 Physical Properties of Minerals
Cleavage is described by: Number of planes Angles between adjacent planes These are constant for a particular mineral

25 Physical Properties of Minerals
Cleavage (1 direction): Example: mica

26 Physical Properties of Minerals
Cleavage (2 directions): orthoclase amphibole

27 Physical Properties of Minerals
Cleavage (3 directions): halite calcite

28 Physical Properties of Minerals
Cleavage (4 directions): fluorite

29 Physical Properties of Minerals
Fracture: minerals that do not exhibit cleavage are said to fracture smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture Quartz

30 Physical Properties of Minerals
Specific gravity: weight of a mineral divided by weight of an equal volume of water metallic minerals tend to have higher specific gravity than non-metallic minerals Galena SG=7.5 Quartz SG=2.67

Specific Gravity S.G. is an easily measured physical property that can be readily estimated. In general, sulphides and oxides have much higher specific gravities than silicates. MINERAL GROUP MINERAL SPECIFIC GRAVITY Framework Silicate Quartz Feldspar Sheet Silicate Mica Chain Silicate Amphibole Pyroxene Isolated Silicate Olivine Garnet Sulphide Sphalerite 4.0 Chalcopyrite 4.2 Pyrite 5.0 Oxide Magnetite 5.2 Hematite 5.3 Galena 7.2 Pitchblende 9.5 Element Native Gold 12.4

32 Physical Properties of Minerals
Other properties: reaction with hydrochloric acid (calcite fizzes) taste (halite tastes salty) feel (talc feels soapy, graphite feels greasy) magnetism (magnetite attracts a magnet)

33 Mineral Groups Rock-forming minerals
~30 common minerals make up most rocks in Earth’s crust Composed mainly of the 8 elements that make up over 98% of the crust

34 SILICATES Mineral Groups Common cations that bond with silica anions
Element Abundances Silica (SiO4)4- SILICATES Common cations that bond with silica anions All others: %

35 Common Silicate mineral groups
formula cleavage Silicate structure Olivine (MgFe)2SiO4 none Single tetrahedron Pyroxene (Mg, Fe) SiO3 two cleavage planes at 900 chains Amphiboles: Eg. hornblende (Ca2Mg5)Si8O22(OH)2 Two planes at 600and 1200 Double chains Mica Muscovite KAl3Si3O10(OH)2 One plane sheets Biotite K(MgFe)3Si3O10(OH)2 Feldspars:K-feldspar Orthoclase, microcline KAlSi3O8 Two planes at 900 Three dimensional networks Plagioclase (Ca,Na)AlSi3O8 Quartz SiO2 Three dimensional network

36 Common Non Silicate mineral groups
member formula uses Oxides Sulphides Sulfates Native elements Halides Carbonates Magnetite Haematite Corundum Galena Sphalerite Pyrite Gypsum Anhydrite Gold Silver Copper Sulfur Graphite Halite Flourite Calcite Fe3O4 Fe2O3 Al2O3 PbS ZnS FeS2 CaSO4.H2O CaSO4 Au Ag Cu S C NaCl CaF2 CaCO3 Ore of iron Abrasive Ore of lead Ore of zinc Fool’s gold Used for plaster Precious metal Used for Wires Used in chemicals pencils Common salt Used in cement

37 Mineral Groups Silicates (most abundant)
Non-silicates (~8% of Earth’s crust): Oxides O2- Carbonates (CO3)2- Sulfides S2- Sulfates (SO4)2- Halides Cl-, F-, Br- Native elements (single elements; e.g., Au)

38 Mineral Groups – Silicates
Tetrahedron fundamental building block 4 oxygen ions surrounding a much smaller silicon ion Silicon-oxygen tetrahedron (SiO4)4-

39 Mineral Groups – Silicates
Joining Silicate Structures How tetrahedra may be linked: independent tetrahedra single chains double chains sheets 3-D framework

40 Mineral Groups – Silicates –

41 Mineral Groups – Silicates
Olivine Group dark silicates (Fe-Mg)  ferromagnesian No cleavage

42 Composition Magnesium iron silicate. The series ranges from the magnesium end member, Forsterite, through the intermediate member, Olivine (also known as Chrysolite), to the iron end member, Fayalite The Olivine group is composed of three minerals, with the following formulas: Forsterite = Mg2SiO4 Olivine (Chrysolite) = (Mg,Fe)2SiO4 Fayalite = Fe2SiO4 The intermediate variety, Olivine, is not scientifically recognized as a separate mineral, but is nevertheless mentioned.

43 Color Olive-green, yellow-green, light green, yellow, yellow-brown, brown, gray, white Streak Colorless Hardness 6½ - 7 Crystal Forms and Aggregates Usually occurs as rounded grains, in dense aggregates of grainy crystals, and as fractured masses. Transparency Transparent to translucent Specific Gravity Luster Vitreous Cleavage none Fracture Conchoidal Tenacity Brittle

44 Uses The variety Peridote is a famous gem. It creates a distinctive, yellow-green to olive-green gem that is well known. It is the birthstone for August. Olivine is also used as a flux for making steel, and is an ore of magnesium. Striking Features Color, localities, and hardness Complex Tests Soluble in hydrochloric acid

45 Mineral Groups – Silicates
Pyroxene Group Ferromagnesian / dark silicates (Fe-Mg) Augite 2-directions of cleavage (at nearly 90 degrees)

46 Minerals The typical pyroxene structure contains chains of SiO3 tetrahedrons The slope of the tetrahedral pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90o degrees (actually 93o and 87o).

47 Pyroxene minerals are common in in meteorites and the extrusive igneous rock called basalt. There are many different types of pyroxene including augite, wollastonite, diopside, enstatite, and hypersthene. All of the types contain Si2O6 but some have sodium (Na) while others have iron (Fe), magnesium (Mg), or a combination of these three elements . The general properties of the more common pyroxene minerals, such as augite, are listed below. Shape:Orthrorhombic or Monoclinic Luster: Glassy or metallic Color: Black Streak: White, light green or light brown Hardness: on Mohs hardness scale Cleavage: Two planes that meet at nearly a 90-degree angle Fracture: Most have uneven and brittle fractures.

48 Mineral Groups – Silicates
Amphibole Group Ferromagnesian / dark silicates (Ca, Fe-Mg) Hornblende 2-directions of cleavage (not at 90 degrees)

49 There are several different minerals within the amphibole group, but the most common type is hornblende. You can find small crystals of hornblende in many types of igneous rocks. They often look like little dark specks. Hornblende (Ca2Mg5)Si3O22(OH)2 Shape: Monoclinic (crystals look like short, six-sided columns) Luster: Glassy or milky Color: Black or dark green, translucent to opaque Streak: Grey-green or grey-brown Hardness: 5-6 Cleavage: Two planes that meet at a 124-degree angle Fracture: Uneven brittle fracture

50 Mineral Groups – Silicates
Mica Group and Clay Minerals light silicates (K, Al)  non-ferromagnesian Muscovite 1-direction of cleavage

51 Minerals Micas and Clay Minerals
Sheets of tetrahedra are the building blocks. Aluminum is also involved in thesesheet structures which are charge-balanced by the cations Mg, Na and K. most common mica minerals:muscovite , biotite

52 Mica minerals make some rocks sparkle
Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book.

53 Biotite K(MgFe)3Si3O10(OH)2 Shape: Monoclinic. Forms flat plates. Luster: Pearly, metallic Color: Dark brown, dark green or black Streak: White Hardness: 2.5-3 Cleavage: Yes, one plane of cleavage Fracture: The mineral is rather flexible and so it doesn’t fracture very easily. In fact you can bend it very far before it breaks. Muscovite KAl3Si3O10 (OH)2 Color: Colorless or lightly tinted Hardness: 2-3 on Mohs Hardness Scale Cleavage: Yes, one plane of cleavage Fracture: This mineral is also flexible and doesn’t fracture very easily.

54 Mineral Groups – Silicates
Feldspar Group light silicates (K-Na-Ca, Al) K-feldspar Most common mineral group Orthoclase Plagioclase 2-directions of cleavage (at 90 degrees) Ca/Na-feldspar

55 Minerals Feldspar group
A second group of alumino-silicates, tetrahedra form three-dimensional frameworks with Ca, Na and K as the balancing cations. The very abundant feldspar are K-Na bearing alkali The K-feldspars or alkali felspars: Microcline, (Potassium aluminum silicate) Orthoclase, (Potassium aluminum silicate)

56 Feldspar is the most common mineral in the Earth’s crust, so you are very likely to find it in the rocks you collect! It is found it all of the three rock types, but is most common in intrusive igneous rocks like granite where the crystals look white or pink. There are several types of feldspar. The characteristics of the two most common types are listed below. These two common types of feldspar are difficult to tell apart besides their color. Color can be helpful, but beware because the same mineral can often have different colors. The sure way to tell these two apart is by looking at the crystal surfaces for thin parallel groves called striations. Plagioclase feldspar has striations but orthoclase feldspar does not.

57 Orthoclase K AlSi3O8 Shape: Monoclinic (Flat tabular or prism-shaped crystals) Luster: Glassy or pearly Color: Cream to pink Streak: White Hardness: 6 on Mohs Hardness Scale Cleavage: perfect Fracture: brittle Plagioclase CaNaAlSi3O8 Shape: Triclinic (Single prism-shaped crystals are very rare. You are much more likely to find many crystals that have grown together in a mass. Color: White to gray Hardness: 6-6.5 Cleavage: perfect Fracture: brittle

58 Mineral Groups – Silicates
Quartz light silicates (pure SiO2) no cleavage (conchoidal fracture) hard, resistant to weathering Quartz

59 Quartz is one of the most common mineral in Earth’s crust!
Silica (Si) and Oxygen (O) are the only elements within pure quartz. Quartz can be found in all sorts of rocks. Most sand is made of quartz because it is hard and does not weather away easily. Some pieces of quartz are white like milk but most are clear like glass, sometimes with a little pink or grey tinge of color. Quartz Shape: Trigonal (Perfect crystals are usually 6-sided prisms with a pyramid shape at the end. However, it is much more common to find many crystals that have grown in a mass or broken crystals.) Luster: vitreous Color: Colorless or white. Some varieties are pink or smoky. Streak: White Hardness: 7 Cleavage: None Fracture: Conchoidal

60 Minerals Quartz Silica tetrahedra alone can form a neutral three-dimensional framework structure with no need for other cations. This arrangement forms a very stable structure popular as ornamental stone and as gemstones Amethyst is the purple gemstone variety. Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. Milky Quartz is the cloudy white variety. Rock crystal is the clear variety that is also used as a gemstone. Rosey Quartz is a pink to reddish pink variety. Smoky quartz is the brown to gray variety.


62 Mineral Groups Non-ferromagnesian Silicates (K, Na, Ca, Al)
Silicates (Fe, Mg) Oxides Carbonates Sulfides/sulfates Native elements

63 Minerals There are a few important groups of non-silicate minerals.
Only the carbonates are significant as rock-forming minerals. The remaining mineral groups are often ore minerals and provide economic sources for various elements. The important non-silicate groups are: Carbonates Evaporites Oxides Sulphides Phosphates

64 Minerals Non silicates: Carbonates Co3
The important carbonates are the minerals calcite and dolomite. Both are significant rock-forming minerals. The calcite group Calcite (Calcium Carbonate) Magnesite(Magnesium Carbonate) Rhodochrosite (Manganese Carbonate) Siderite(Iron Carbonate) Smithsonite (Zinc Carbonate)

65 Minerals The most famous halide mineral, halite (NaCl) or rock salt
Non silicates: Evaporites: including the minerals halite, and fluorite; Sulphates including the minerals gypsum and anhydrite. The most famous halide mineral, halite (NaCl) or rock salt

66 Minerals Non silicates: Evaporites Fluorite: CaF2, Calcium Fluoride

67 Minerals Non silicates: Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate

68 Minerals Non silicates: Oxides
oxides (hematite and magnetite) Fe2O3, Iron Oxide hydroxides (limonite and goethite) important minor constituents in rocks. aluminum oxide bauxite can also occur as a rock-forming mineral. oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium.

69 Minerals Non silicates: Sulphides
The mineral pyrite is the only sulphide that occurs commonly in rocks. Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc. FeS2, Iron Sulfide

70 Minerals Non silicates: Sulphides
The mineral pyrite (FeS2) is the only sulphide that occurs commonly in rocks. Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc. Galena, Chalcopyrite

71 Minerals Non silicates:
Phosphates are relatively rare. The only important phosphate mineral is apatite. Ca2Fe(PO4)2 - 4H2O, Hydrated Calcium Iron Phosphate

72 Common minerals the most common minerals you'll find in rocks (rock forming minerals) This pile contains plagioclase feldspar, potassium feldspar, quartz, muscovite mica, biotite mica, amphibole, olivine, and calcite.

73 Acknowledged sources –

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