Minerals - SCHOOLinSITES

Minerals - SCHOOLinSITES

Minerals Text ref. Ch.4 (pg. 76) Contents What is a mineral? Identifying Minerals Symmetry Operations

Minerals Text ref., Ch.4 p.77-83 Objectives Define a mineral. Describe how minerals form.

Identify the most common elements in Earths crust. Mineral Characteristics Naturally occurring Inorganic solid Chemical composition

Crystalline structure Mineral? Mineral? Mineral?

Mineral? Mineral? Mineral?

Minerals: Naturally-Occurring and Inorganic Made by natural physical and chemical processes, rather than by man-made processes. Minerals are not living were never living at any portion of their existence.

Coal: organic origin, therefore not a mineral Sugar: organic, therefore not a mineral Salt: inorganic, therefore mineral

Minerals: Solids with Specific Compositions Solid: has definite shape and volume. Liquids and gases are not considered minerals Minerals have a specific chemical

composition CaCl2: calcium carbonate Au: gold

Minerals with variable compositions Some minerals may have variations in total numbers of atoms, but ratio of atoms in chemical composition

remains constant. Ex. Watermelon tourmaline Minerals: Definite Crystalline

Structure Atoms in minerals are arranged in regular geometric patterns repeated many times Crystals are solids with this regular repeating pattern. Minerals from Magma

Magma is a molten material found beneath the Earths surface. As magma rises it cools. Minerals form as this cooling process occurs. Elements found in the magma determine what minerals form. Slow-cooling magma produces minerals with

large crystals, whereas fast-cooling magma produces minerals with small crystals Minerals from Solution Crystallization can also occur as minerals fall out of

solution. Solvent usually water

Solute is the mineral Mineral Groups 3000 minerals can be found in the Earths crust Only 30 of these are common.

Majority of elements are made of the following elements Common Mineral Groups Native Elements Oxides and hydroxides Halides

Carbonates Sulfates Silicates Sulfides Copper (Cu) Gold (Au) Hematite (Fe2O3) Brucite

(Mg(OH)2) Halite (NaCl) Calcite (CaCO3) Anhydrite (CaSO4) Olivine (Mg2SiO4) Pyrite (FeS2)

Silicates Minerals containing silicon and oxygen Make up approximately 96% of the minerals found in the Earths crust Ex. Feldspar, quartz

olivine Silica Structures Single chain pyroxene

Silica Structures Double chain hornblende Silica Structures

Silica sheet Biotite and muscavite Carbonates Minerals containing the carbonate ion

(CO3-2) Commonly contain a metal ion plus carbonate ion Ex: calcite (CaCO3) Malachite (Cu2CO3(OH)2) Oxides

Compounds containing an oxide (O-2) and a metal. Ex: Hematite (Fe2O3) and magnetite (Fe3O4) Many oxides are commonly sought for

their valuable minerals. Sulfides, Sulfates, Halides, and Native Elements Sulfides contain the sulfide ion (S-2) Sulfates contain the sulfate ion (SO4-2)

Halides contain a halogen ion such as chloride (Cl-) or fluoride (F-) Native elements are made up of one element only, such as silver (Ag) or gold (Au) See Appendix H for additional information on minerals and their compositions

Identifying Minerals Text ref. Ch.4.2, pg. 84-91 Objectives Classify minerals according to their physical and chemical properties.

Identify different types of minerals. Discuss how minerals are used. Mineral Identification Geologists use both the physical and chemical properties of mineral samples for identification.

Color Luster Texture Streak Hardness Cleavage and Fracture Density and Specific Gravity

Color Often caused by trace elements in the mineral One of the least reliable methods of identification

Luster Defined as the way light is reflected from the surface of a mineral. Described as metallic or nonmetallic Texture Describes how minerals feel to the touch

Minerals may classified as having the following textures

Smooth Rough Ragged Greasy Soapy

Glassy Streak Color of a mineral when it is broken up and powdered. Sometimes streak will not match up the color of the mineral itself.

Streak can be a valuable means of identification. Hardness Measure of how easily a mineral can be scratched. Hardness is determined by the strength of

the chemical bonds that compose the mineral Mohs hardness scale is used to classify the hardness of a mineral sample One of the most reliable methods of mineral identification

Mohs Hardness Scale Hardness Hardness of common objects Talc

1(softest) Gypsum 2

Fingernail(2.5) calcite 3 Piece of copper(3.5)

Fluorite 4 Iron nail(4.5)

Apatite 5 Glass(5.5) Feldspar

6 Steel file(6.5) Quartz

7 Streak plate(7) Topaz 8

Scratches quartz Corundum 9

Scratches quartz Diamond 10(hardest) Scratches all common

materials Cleavage Atomic arrangement also determines how easily a mineral will break. Minerals that split or break along one or more flat planes possess a property

known as cleavage. Mineral ID can be made by counting the # of cleavage planes and the angles that are formed. Fracture Minerals that break with rough or jagged

edges are said to have fracture. Minerals that possess fracture do not possess cleavage planes. Concoidial fracturing describes fracturing that produces arc-like patterns resembling clam shells

Density and Specific Gravity Density is a particularly useful tool in mineral identification D = M/V Each mineral has its own density, based on its atomic structure. Specific Gravity is the ratio of the weight of

a substance to an equal volume of water at 4C Special Properties Some minerals possess special properties that may be used in identification.

Optical properties Magnetism Chemical reactivity

Mineral Uses Used for a variety of purposes.

Electronics Jewelry Cars Buildings Medicines

Etc Ores Minerals are considered to be ores if they can be mined for a profit.

Hematite is an ore of iron Bauxite is an ore of aluminum Mines Areas of the Earths crust containing ores. Mining methods vary, but all cause some

form of ecological damage to their surroundings. Gems Gems are valuable minerals that are prized for their rarity and beauty. Cut, polished, and used for jewelry

Trace elements can increase the value of one form of a mineral to another. Quartz varieties: Sand at the beach: little value Amethyst: semiprecious stone

Introduction to Symmetry Operations Symmetry Operations and Elements Rotation

Reflection Inversion if an object can be rotated about an axis and repeats itself every 90o of rotation then it is said to have an axis of 4-fold rotational symmetry

The axis along which the rotation is performed is an element of symmetry referred to as a rotation axis 1-Fold Rotation Axis An object that requires rotation of a full 360o in order to restore it to its

original appearance has no rotational symmetry. Since it repeats itself 1 time every 360o it is said to have a 1-fold axis of rotational symmetry.

2-fold Rotation Axis - If an object appears identical after a rotation of 180o, that is twice in a 360o rotation, then it is said to have a 2-fold rotation axis (360/180 = 2). Note that in these examples the axes we

are referring to are imaginary lines that extend toward you perpendicular to the page or blackboard. A filled oval shape represents the point where the 2-fold rotation axis intersects the page.

3-Fold Rotation AxisObjects that repeat themselves upon rotation of 120o are said to have a 3-fold axis of rotational symmetry (360/120 =3), and they will repeat 3

times in a 360o rotation. A filled triangle is used to symbolize the location of 3-fold rotation axis. 4-Fold Rotation Axis - If an object repeats itself

after 90o of rotation, it will repeat 4 times in a 360o rotation, as illustrated previously. A filled square is used to symbolize the location of 4-fold axis of rotational

symmetry. 6-Fold Rotation Axis - If rotation of 60o about an axis causes the object to repeat itself, then it has 6fold axis of rotational

symmetry (360/60=6). A filled hexagon is used as the symbol for a 6fold rotation axis. Although objects themselves may appear to have 5-fold, 7-fold, 8-fold, or higher-fold

rotation axes, these are not possible in crystals. Note that if we try to combine objects with 5-fold and 8-fold apparent symmetry, that we cannot combine them in such a way that they completely fill space.

Mirror Symmetry A mirror symmetry operation is an imaginary operation that can be performed to reproduce an object. the plane of the mirror is an element of symmetry referred to as a mirror plane, and is symbolized with the letter m

Center of Symmetry Another operation that can be performed is inversion through a point. lines are drawn from all points on the object through a point in the center of the object, called a symmetry center

(symbolized with the letter "i") If an object has only a center of symmetry, we say that it has a 1 fold rotoinversion axis. Such an axis has the symbol 1 Rotoinversion

Combinations of rotation with a center of symmetry perform the symmetry operation of rotoinversion. 2-fold Rotoinversion - The operation of 2fold rotoinversion involves first rotating

the object by 180 then inverting it through an inversion center. 3-fold Rotoinversion - This involves

rotating the object by 120o (360/3 = 120), and inverting through a center. 4-fold Rotoinversion - This involves

rotation of the object by 90o then inverting through a center. 6-fold Rotoinversion - A 6-fold rotoinversion axis ( )

involves rotating the object by 60o and inverting through a center. Combinations of Symmetry Operations

32 possible combinations of symmetry elements. These 32 combinations define the 32 Crystal Classes. Every crystal must belong to one of these 32 crystal classes.

In this example we will start out with the crystal shown here. Note that this crystal has rectangular-shaped sides with a square- shaped top and bottom. The squareshaped top indicates that

there must be a 4-fold rotation axis perpendicular to the square shaped face. This is shown in the diagram. 1 - 4-fold rotation axis (A4)

4 - 2-fold rotation axes (A2), 2 cutting the faces & 2 cutting the edges. 5 mirror planes (m), 2 cutting across the faces, 2 cutting through the edges, and one cutting horizontally through

the center. Note also that there is a center of symmetry (i). The symmetry content of this crystal is thus:

i, 1A4, 4A2, 5m

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