Chapter 5- Minerals (Week 3)

Question 1

What is a mineral?

Answer 1

Definition: A mineral is a naturally occurring solid composed of specific elements, arranged in a distinctive repeating three-dimensional structure.

Characteristics:
-Naturally Occurring: Formed from substances and conditions found in nature.
-Solid: Generally solid at 25°C (with exceptions for substances defined as minerals before 1959).

Exclusions: Anthropogenic materials (made only by humans) and substances produced by natural processes acting upon anthropogenic materials are not considered minerals.

Examples: Common minerals include graphite, salt, plaster, gold, and others found in everyday items.

Question 2

What does “naturally occurring” mean in the context of mineral definition?

Answer 2

In the context of mineral definition, “naturally occurring” indicates that minerals can form from substances and under conditions found in nature. Anthropogenic materials, or substances produced solely by humans, do not qualify as minerals based on this criterion.

Question 3

What does “specific elements” mean in the context of mineral definition?

Answer 3

In the context of mineral definition, “specific elements” implies that minerals have a well-defined chemical formula or composition. Deviation from this formula would result in a different mineral. For example, the mineral pyrite has the formula FeS2, signifying two atoms of sulfur for each atom of iron.

Question 4

What is solid solution in the context of minerals?

Answer 4

Solid solution refers to a variation in the composition of a mineral within a specific range. It allows for the substitution of one element for another within the mineral’s structure. An example is the mineral olivine, with the formula (Fe,Mg)2SiO4, allowing a range of compositions between Fe2SiO4 and Mg2SiO4, with any proportion of iron and magnesium in between.

Question 5

Why are all minerals considered crystals?

Answer 5

All minerals are considered crystals because the atoms within them are arranged in a specific repeating three-dimensional structure or lattice. This regular structure is a defining characteristic of minerals. For instance, the mineral halite, or table salt, exhibits a crystal lattice where atoms of sodium (Na) alternate with atoms of chlorine (Cl), forming a consistent structure. Even small crystals have lattices that extend in three dimensions, repeating thousands of times.

*image 1

Question 6

What is the term for substances that have mineral-like properties but lack a regular crystalline structure?

Answer 6

Substances that have mineral-like properties but lack a regular crystalline structure are called mineraloids. Opal is an example of a mineraloid. While opal has a specific chemical composition (SiO2·nH2O) and forms naturally, its structure consists of closely packed spheres instead of a lattice.

*image 1

Question 7

Can opal be considered a mineral?

Answer 7

Opal is not classified as a mineral but as a mineraloid. While it has mineral-like characteristics, including a specific chemical composition, it lacks the regular crystalline structure typical of minerals. Opal’s structure consists of closely packed spheres, distinguishing it from minerals with crystalline lattices.

*Image 2

Question 8

What are the three main particles that make up atoms, and what are their charges?

Answer 8

The three main particles that make up atoms are protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.

Question 9

Why is it possible to have more than one proton in an atomic nucleus despite protons having a positive charge that repels each other?

Answer 9

Neutrons, which have no charge, hold protons together in an atomic nucleus, allowing for the presence of multiple protons. While protons repel each other due to their positive charge, neutrons act as a stabilizing force within the nucleus. The combination of protons and neutrons forms the nucleus at the center of an atom

Question 10

What are isotopes?

Answer 10

Isotopes are forms of an element that have the same number of protons but different numbers of neutrons. They can exist for various elements, resulting in atoms with similar chemical properties but different atomic masses

Question 11

What determines the element an atom will be, and what is the term for the number of protons in an atom?

Answer 11

The element an atom will be is determined by the number of protons it possesses. This number is called the atomic number.

Question 12

What is the mass number of an atom, and how does it relate to the atomic number?

Answer 12

The mass number of an atom is the total number of protons and neutrons in its nucleus. It distinguishes between isotopes of an element. While the atomic number (number of protons) defines the element, the mass number provides information about the isotope’s atomic mass.

Question 13

How are isotopes of an element denoted, and can you provide an example?

Answer 13

Isotopes of an element are denoted by placing the mass number as a subscript in front of the symbol for that element. For example, the isotopes of hydrogen are 1H (1 proton), 2H (1 proton + 1 neutron), and 3H (1 proton + 2 neutrons).

*image 4

Question 14

Why do most of the lightest elements (up to oxygen) have the same number of neutrons as protons in their nuclei?

Answer 14

For most of the 16 lightest elements, the number of neutrons is equal to the number of protons in their nuclei. However, for heavier elements, especially those with more concentrated protons, more neutrons are needed to counteract the repulsion between positively charged protons and keep the nucleus stable.

Question 15

Why is uranium (U) considered radioactive, and what happens during its radioactive decay?

Answer 15

Uranium is radioactive because its nucleus is unstable and will eventually split apart, a process known as radioactive decay. During decay, the nucleus releases energy, and what remains of the nucleus has fewer protons, leading to a transformation into a different element. The most common isotope of uranium is 238U, with 92 protons and 146 neutrons.

Question 16

Why are the outermost electrons crucial for chemical bonding, and can you provide an example of an element with incomplete outer shells?

Answer 16

The outermost electrons, or valence electrons, are crucial for chemical bonding as they can interact with the outer electrons of nearby atoms. For example, lithium (Li) is an element with incomplete outer shells, and its outermost electrons can participate in forming chemical bonds with other atoms.

*image 5

Question 17

How many electrons can the first and subsequent electron shells hold, and what is the maximum number of outermost electrons an atom can have for chemical bonding?

Answer 17

The first shell can hold up to two electrons, and subsequent shells can hold up to eight electrons each. There are never more than eight outermost electrons influencing chemical bonding interactions.

Question 18

What is the significance of a full outer shell for atoms, and how many electrons does the first shell of an atom aim to have?

Answer 18

Atoms seek to have a full outer shell, and for hydrogen and helium, a full outer shell means two electrons. For other elements, it means having 8 electrons in the outer shell

Question 19

How do atoms achieve a full outer shell, and why is this process significant in the study of minerals?

Answer 19

Atoms achieve a full outer shell by transferring or sharing electrons with other atoms in chemical bonds. This process is significant in the study of minerals because the type of chemical bond influences many physical and chemical properties of minerals.

Question 20

What determines the type of chemical bond formed between atoms, and why is it crucial in understanding mineral properties?

Answer 20

The type of chemical bond formed between atoms is determined by how electrons are transferred or shared. It is crucial in understanding mineral properties because the type of bond influences various characteristics of minerals.

Question 21

How many electrons can the first shell of an atom hold, and why is it relevant in the context of chemical bonding?

Answer 21

The first shell of an atom can hold up to two electrons. This is relevant in chemical bonding as the outermost electrons, or valence electrons, determine how atoms bond with each other.

Question 22

Explain the process of forming an ionic bond with the example of halite (NaCl).

Answer 22

In the example of halite (NaCl), sodium (Na) readily gives up an electron to achieve a full outer shell, becoming a positive ion or cation. Chlorine (Cl) accepts the electron to fill its outer shell, becoming a negative ion or anion. The attraction between these oppositely charged ions creates an ionic bond in NaCl.

Question 23

What is an ion, and how do ions form in the context of ionic bonds?

Answer 23

An ion is a charged atom that forms when an atom gains or loses electrons. In ionic bonds, atoms transfer electrons, resulting in positively charged ions (cations) and negatively charged ions (anions).

You can remember that a cation is positive by remembering that a cat has paws (paws sounds like “pos” in “positive”). You could also think of the “t” in “cation” as a plus sign.

Question 24

Why do sodium and chlorine ions stick together in an ionic bond?

Answer 24

Sodium and chlorine ions stick together in an ionic bond due to the attraction between oppositely charged ions. The positive charge of the sodium ion (cation) attracts the negative charge of the chlorine ion (anion).

*image 5

Question 25

What is the role of electrons in the formation of an ionic bond?

Answer 25

In an ionic bond, electrons transfer from one atom to another. This electron transfer results in the formation of positive and negative ions, and the attraction between these ions creates the ionic bond.

Question 26

Explain how covalent bonds form, using the example of chlorine gas (Cl2) and carbon.

Answer 26

In covalent bonding, atoms share electrons to achieve a full outer shell. In the case of chlorine gas (Cl2), two chlorine atoms share electrons to complete their outer shells. Carbon also participates in covalent bonding by sharing electrons, as seen in the formation of strong covalent bonds in the mineral diamond. *image 6

Question 27

Why does carbon prefer covalent bonding over ionic bonding?

Answer 27

Carbon prefers covalent bonding over ionic bonding because gaining or losing four electrons to achieve a filled outer shell would create too great a charge imbalance. Covalent bonding allows carbon to share electrons and achieve a stable configuration. *image 7

Question 28

How are carbon atoms arranged in the mineral diamond, and what type of bonds do they form?

Answer 28

In the mineral diamond, carbon atoms are linked together in a three-dimensional framework. Each carbon atom is bonded to four other carbon atoms through very strong covalent bonds. *image 8

Question 29

What is the difference between ionic and covalent bonds?

Answer 29

Ionic bonds involve the transfer of electrons between atoms, creating oppositely charged ions that attract each other. Covalent bonds involve the sharing of electrons between atoms to achieve a stable electron configuration.

Question 30

Describe the bonding in the mineral graphite and explain why it has a soft texture.

Answer 30

In graphite, carbon atoms are covalently bonded within layers, but weak Van der Waals forces hold the layers together. This structure gives graphite its soft texture as the layers can slide over each other easily.

Question 31

What are Van der Waals forces, and how do they contribute to the properties of materials like graphite?

Answer 31

Van der Waals forces are weak attractive forces between molecules. In graphite, these forces are responsible for holding the layers together. While the covalent bonds within layers are strong, the weak Van der Waals forces between layers allow them to slide easily, giving graphite its unique properties.

Question 32

Compare the charge distribution in a water molecule to that in a carbon dioxide molecule, and explain how this affects their properties.

Answer 32

In a water molecule, the bent shape causes an asymmetric charge distribution with hydrogen atoms on one side and oxygen on the other, leading to a polar molecule. In carbon dioxide, the linear shape results in a symmetric distribution. The asymmetry in water molecules contributes to properties like hydrogen bonding and high surface tension *image 9

Question 33

Describe metallic bonding and mention two important properties of metals associated with this type of bonding.

Answer 33

Metallic bonding occurs in metallic elements where outer electrons are relatively loosely held. In this type of bonding, dissociated electrons can move freely between atoms. Two important properties of metals due to metallic bonding are electrical conductivity and malleability.

Question 34

Why do metals exhibit electrical conductivity and malleability? How does metallic bonding contribute to these properties?

Answer 34

In metallic bonding, dissociated electrons can move freely between atoms. This mobility of electrons allows metals to conduct electricity. Additionally, the ability of atoms to slide past each other while maintaining the metallic bond contributes to the malleability of metals. *image 10

Question 35

How are minerals organized, and what is the basis for this organization?

Answer 35

Minerals are organized based on the anion or anion group they contain. This is because the anion or anion group has the most significant impact on the properties of the mineral.

Question 36

Which anion or anion group is the most abundant in the Earth's crust and mantle?

Answer 36

Silicates, with the anion group SiO44-, are the most abundant group in the Earth's crust and mantle.

Question 37

What are some examples of mineral groups, and how are they classified?

Answer 37

Mineral groups are classified based on the anion or anion group they contain. Examples include oxides, sulfides, sulfates, halides, carbonates, phosphates, and silicates.

Question 38

What is the basis for classifying minerals as oxide minerals?

Answer 38

Oxide minerals are classified based on the oxygen anion (O2–) they contain.

Question 39

Can you provide examples of oxide minerals and their uses?

Answer 39

Examples of oxide minerals include hematite and magnetite (ores of iron), corundum (used as an abrasive and as a gemstone in ruby and sapphire varieties), limonite, and bauxite (ores of iron and aluminum, respectively). *image 11

Question 40

What is a hydroxide mineral, and can you provide examples?

Answer 40

A hydroxide mineral is one in which oxygen is combined with hydrogen to form the hydroxyl anion (OH–). Examples include limonite and bauxite, which are ores of iron and aluminum, respectively.

Question 41

What is the defining feature of sulphide minerals, and can you name some examples?

Answer 41

Sulphide minerals are characterized by the presence of the sulphide anion (S2-). Examples include galena, sphalerite, chalcopyrite, molybdenite (important ores of lead, zinc, copper, and molybdenum, respectively), pyrite, bornite, stibnite, and arsenopyrite. *image 12

Question 42

What is a common visual characteristic of sulphide minerals?

Answer 42

Sulphide minerals tend to have a metallic sheen.

Question 43

How do sulphate minerals typically form, and what can a deposit of sulphate minerals indicate about the past environment?

Answer 43

Sulphate minerals often form when sulphate-bearing water evaporates. A deposit of sulphate minerals may indicate that a lake or sea has dried up at that location.

Question 44

Can you name some sulphate minerals and the cations they contain?

Answer 44

Examples of sulphate minerals include anhydrite and gypsum (calcium sulphates), barite (barium sulphate), and celestite (strontium sulphate). In these minerals, the cation has a +2 charge, balancing the -2 charge on the sulphate ion. *image 13

Question 45

What are halide minerals, and what are the anions they contain?

Answer 45

Halide minerals are those that contain anions from the halogen group, including chlorine, fluorine, and bromine. Examples include cryolite, fluorite, and halite. Halide minerals are typically formed by ionic bonds, and some may also form when mineral-rich water evaporates. *image 14

Question 46

Which anion group combines with +2 cations to form minerals such as calcite, magnesite, dolomite, and siderite?

Answer 46

The carbonate anion group (CO3^2-) combines with +2 cations to form minerals such as calcite, magnesite, dolomite, and siderite. *image 15

Question 47

What is the anion group associated with the apatite group of phosphate minerals?

Answer 47

The phosphate minerals in the apatite group are associated with the PO4^3- anion. *image 16

Question 48

Can you provide examples of native element minerals?

Answer 48

Examples of native element minerals include gold, copper, silver, and sulfur. *image 17

Question 49

What is the basic building block of many important minerals in the crust and mantle?

Answer 49

The basic building block of many important minerals in the crust and mantle is the silicate tetrahedron (SiO44-). a four-sided pyramid shape with oxygen at each corner and silicon in the middle Silicon has a charge of +4, and oxygen has a charge of -2, so the total charge of the silicate anion is -4. *image 18

Question 50

What is the simplest silicate structure, and which mineral exhibits it?

Answer 50

The simplest silicate structure is composed of isolated tetrahedra, and the mineral olivine exhibits this structure. is composed of isolated tetrahedra bonded to iron and/or magnesium ions

Question 51

What is the primary bonding mechanism in halide minerals?

Answer 51

Halide minerals are made of ionic bonds.

Question 52

How are isolated tetrahedra arranged in olivine, and what cations balance the charge of the tetrahedra?

Answer 52

Isolated tetrahedra in olivine are bonded to iron and/or magnesium ions. The charge of each silica tetrahedron (-4) is balanced by two iron or magnesium cations, each with a charge of +2.

Question 53

Give an example of a carbonate mineral and state the chemical formula of the carbonate anion.

Answer 53

An example of a carbonate mineral is calcite, and the chemical formula of the carbonate anion is CO3^2-.

Question 54

What is an example of a single-chain silicate, and what is its chemical formula?

Answer 54

Pyroxene is an example of a single-chain silicate, and its chemical formula includes compositions such as MgSiO3, FeSiO3, and CaSiO3.

Question 55

How does the structure of chain silicates differ from isolated tetrahedra, and what is the impact on the oxygen-to-silicon ratio?

Answer 55

In chain silicates, silica tetrahedra form a chain, sharing one oxygen with adjacent tetrahedra. This results in a lower oxygen-to-silicon ratio (O:Si) compared to isolated tetrahedra.

Question 56

How does the net charge per silicon atom in pyroxene compare to olivine, and why?

Answer 56

The net charge per silicon atom in pyroxene is less negative than olivine (-2 instead of -4) because fewer cations are needed to balance the charge, as the structure is more "permissive," allowing a wider range of cations to fit.

Question 57

What type of silicate structure is found in amphibole, and how does it differ from pyroxene in terms of chain arrangement?

Answer 57

Amphibole has a double-chain silicate structure, where silica tetrahedra are linked in a double chain. This arrangement results in a lower oxygen-to-silicon ratio compared to pyroxene.

Question 58

How does the oxygen-to-silicon ratio in amphibole affect the number of cations needed to balance the charge, and why is amphibole considered more permissive than pyroxene?

Answer 58

The lower oxygen-to-silicon ratio in amphibole means fewer cations are necessary to balance the charge. Amphibole is considered more permissive than pyroxene, allowing for complex compositions and a wider range of cation substitutions.

Question 59

What is the chemical formula for the hornblende group of amphibole minerals, and what does this formula indicate about the composition of amphibole?

Answer 59

The chemical formula for the hornblende group of amphibole minerals is complex, indicating the potential for diverse compositions in amphibole. The formula shown in (bottom right) highlights this complexity. *image 20

Question 60

What characterizes the structure of sheet silicates like mica, and how do the silica tetrahedra arrange themselves in these minerals?

Answer 60

In sheet silicates such as mica, the silica tetrahedra are arranged in continuous sheets. Each tetrahedron shares three oxygen anions with adjacent tetrahedra, forming a planar arrangement.

Question 61

Why do sheet silicate minerals, particularly micas, have a tendency to split apart in sheets?

Answer 61

Bonding between sheets in sheet silicate minerals, like micas, is relatively weak. This weak bonding accounts for the tendency of these minerals to split apart in sheets.

Question 62

Name two common micas found in silicate rocks, and briefly describe their compositions.

Answer 62

Two common micas are biotite (dark mineral, contains iron and/or magnesium) and muscovite (light in color, contains aluminum and potassium). Both micas belong to the sheet silicate group and have water in their structure in the form of the hydroxyl (OH-) anion. *image 21

Question 63

Name three clay minerals that belong to the sheet silicate group and are commonly found in clay-sized fragments in rocks and soils.

Answer 63

The clay minerals kaolinite, illite, and smectite belong to the sheet silicate group and are commonly found in clay-sized fragments in rocks and soils.

Question 64

What is the distinguishing feature of sheet silicates in terms of their structure, and what are examples of sheet silicate minerals?

Answer 64

The distinguishing feature of sheet silicates is that silica tetrahedra are arranged in continuous sheets, and each tetrahedron shares three oxygen anions with adjacent tetrahedra. Examples of sheet silicate minerals include biotite and muscovite.

Question 65

How are tetrahedra connected in single-chain silicates, and what is an example of a single-chain silicate mineral?

Answer 65

In single-chain silicates, silica tetrahedra form a chain because one oxygen from each tetrahedron is shared with the adjacent tetrahedron. An example of a single-chain silicate mineral is pyroxene.

Question 66

How are tetrahedra connected in double-chain silicates, and what is an example of a double-chain silicate mineral?

Answer 66

In double-chain silicates, the silica tetrahedra are linked in a double chain, with fewer oxygens shared between adjacent tetrahedra. An example of a double-chain silicate mineral is amphibole.

Question 67

In framework silicates, how are tetrahedra connected, and what is an example of a common framework silicate in Earth's crust?

Answer 67

In framework silicates, tetrahedra are connected to each other in three-dimensional structures. A common example of a framework silicate is feldspar.

Question 68

What are the three end-members in the ternary system used to classify feldspars, and how are they named?

Answer 68

The three end-members in the ternary system used to classify feldspars are: -Potassium feldspar (K-feldspar): Named based on the presence of potassium. -Albite (alkali feldspar): Named for its high sodium content. -Anorthite (plagioclase feldspar): Named for its high calcium content. *image 22

Question 69

What is the chemical composition of quartz, and what is its structure based on silica tetrahedra?

Answer 69

Quartz has a chemical composition of SiO2, and its structure is based on silica tetrahedra. Each silica tetrahedron in quartz is bonded to four other tetrahedra in a three-dimensional framework, resulting in a silicon-to-oxygen ratio of 1:2.

Question 70

How is the charge balanced in quartz, and what type of bonds contribute to its hardness and irregular breakage?

Answer 70

In quartz, the charge is balanced by the one silicon cation having a +4 charge and the two oxygen anions each having a –2 charge. The hardness of quartz and its irregular breakage are a result of the strong covalent/ionic bonds characteristic of the silica tetrahedron. *image 23

Question 71

What are the criteria required for mineral crystals to grow?

Answer 71

For mineral crystals to grow, the elements must be present in sufficient abundance and appropriate proportions, favorable physical and chemical conditions must exist, and there must be sufficient time for atoms to arrange themselves into a lattice structure.

Question 72

How do physical and chemical conditions, including the presence of water, influence mineral formation?

Answer 72

Physical and chemical conditions, such as temperature, pressure, pH, and the presence of water, play a crucial role in mineral formation. The presence of water aids the movement of ions, facilitating larger crystal formation over shorter time periods.

Question 73

How does the rate of cooling affect the crystal size in rocks formed from molten rock (magma)?

Answer 73

Rapid cooling results in the formation of fine-grained rocks with small crystals (less than 1 mm), while slow cooling or the growth of few crystals at a time leads to the development of relatively large crystals.

Question 74

Besides cooling of magma, what are other ways in which minerals can form?

Answer 74

Minerals can form through precipitation from a solution (e.g., hot water flowing underground or evaporation in a lake), precipitation from a gas (e.g., volcanic gases), metamorphism (reactions under high pressures and temperatures), weathering (chemical alteration at Earth's surface), and organic formation (organisms building shells, teeth, and bones).

Question 75

Provide examples of minerals formed through precipitation from a solution and precipitation from a gas.

Answer 75

Oxide minerals such as hematite and hydroxides like limonite are examples of minerals formed through precipitation from a solution. Examples of minerals formed through precipitation from a gas include those deposited from volcanic gases.

Question 76

What is metamorphism, and how does it contribute to the formation of new minerals?

Answer 76

Metamorphism is the process where solid minerals react with each other under high pressures and temperatures, leading to the formation of new minerals through chemical changes and recrystallization.

Question 77

How do organisms contribute to the formation of minerals, and what are some examples?

Answer 77

Organisms contribute to mineral formation by building structures such as shells (calcite or aragonite) and teeth/bones (apatite). Examples include calcite/aragonite in shells and apatite in teeth and bones.

Question 78

Why are minerals considered universal, and how does this universality benefit geology students?

Answer 78

Minerals are universal because a crystal of a specific mineral will have the same properties regardless of its location, whether on Earth, Mars, or a planet orbiting another star. This universality benefits geology students, enabling them to use consistent mineral properties for identification across different planetary bodies.

Question 79

What are some of the mineral properties useful for identification?

Answer 79

Some mineral properties useful for identification include color, streak, lustre, hardness, habit, cleavage or fracture, and density.

Question 80

Explain the significance of color as a mineral property for identification.

Answer 80

Color is one of the mineral properties used for identification, although it can vary. However, some minerals have distinctive colors that aid in their recognition.

Question 81

What is streak, and how is it different from the color of a mineral?

Answer 81

Streak is the color of a mineral in powdered form, obtained by scraping it across a streak plate. It may differ from the mineral's actual color due to impurities or variations in crystal structure.

Question 82

Define lustre as a mineral property, and provide examples of lustre types.

Answer 82

Lustre refers to the way light interacts with a mineral's surface. Examples of lustre types include metallic (shiny like metal), vitreous (glassy), pearly (pearl-like), and dull (lacking shine)

Question 83

How is hardness measured in minerals, and what scale is commonly used for hardness?

Answer 83

Hardness is measured using the Mohs scale, which ranks minerals from 1 (softest, talc) to 10 (hardest, diamond). It is determined by a mineral's ability to scratch or be scratched by other substances.

Question 84

Define the terms "habit" and "cleavage" as mineral properties.

Answer 84

"Habit" refers to the general shape or form of a mineral, while "cleavage" refers to the way a mineral breaks along planes of weakness.

Question 85

Differentiate between cleavage and fracture as mineral properties.

Answer 85

Cleavage is the way a mineral breaks along planes of weakness, producing smooth, flat surfaces. Fracture, on the other hand, is the way a mineral breaks in irregular or jagged patterns.

Question 86

Why is color considered a useful diagnostic criterion for identifying certain minerals?

Answer 86

Color is considered a useful diagnostic criterion for identifying certain minerals because some minerals have distinctive and characteristic colors that aid in their recognition. *image 24

Question 87

Provide an example of a mineral with a characteristic color.

Answer 87

An example is sulfur, which is always a characteristic bright yellow color.

Question 88

Explain why the color of hematite is not necessarily diagnostic for identification.

Answer 88

Hematite's color is not necessarily diagnostic because it can vary; it may appear as a deep dull red or a metallic silvery black, depending on its form.

Question 89

What factors can cause variations in the color of minerals like quartz?

Answer 89

Variations in the color of minerals like quartz can be caused by varying proportions of trace elements within the mineral or structural defects within the crystal lattice.

Question 90

How does milky quartz obtain its white color, and what causes the grey color in smoky quartz?

Answer 90

How does milky quartz obtain its white color, and what causes the grey color in smoky quartz?

Question 91

What gives amethyst, citrine, and rose quartz their respective colors?

Answer 91

Amethyst and citrine get their colors from trace amounts of iron, and rose quartz gets its pink hue from manganese

Question 92

How do varying proportions of trace elements affect the color of minerals?

Answer 92

Varying proportions of trace elements within a mineral can cause color variations, with different elements imparting different colors to the mineral.

Question 93

What is streak in the context of mineral identification?

Answer 93

Streak, in the context of mineral identification, is the color of a mineral when it is ground to a powder. It is observed by scraping the mineral across a streak plate. The streak of a mineral is obtained by grinding a small amount of the sample to a powder and observing the color of the powder. A streak plate is a piece of unglazed porcelain *image 25

Question 94

Why is streak considered a helpful property in mineral identification?

Answer 94

Streak is considered a helpful property in mineral identification because it provides a more consistent and reliable color representation of a mineral, free from the variability introduced by surface texture and appearance

Question 95

Explain the significance of the similar reddish-brown streak observed in two samples of hematite with different surface appearances.

Answer 95

The similar reddish-brown streak in two samples of hematite with different surface appearances is significant because it shows that streak can be a consistent property, allowing for the identification of minerals based on their powder color, regardless of surface characteristics. *image 26

Question 96

What is lustre in the context of mineral identification?

Answer 96

Lustre, in the context of mineral identification, refers to the way light reflects off the surface of a mineral and the degree to which it penetrates into the interior. Lustre contributes to mineral identification by helping distinguish between metallic and non-metallic minerals.

Question 97

What is the key distinction between metallic and non-metallic lustre?

Answer 97

The key distinction between metallic and non-metallic lustre is that light does not pass through metals, giving them a metallic appearance, while many non-metallic minerals may appear opaque but are actually translucent or transparent when observed in thin slices.

Question 98

Lustre contributes to mineral identification by helping distinguish between metallic and non-metallic minerals.

Answer 98

Examples of non-metallic lustres include glassy, earthy, silky, pearly, and resinous. Glassy lustre is characterized by a shiny, reflective surface, while earthy lustre is characterized by a dull and non-reflective surface.

Question 99

Why do metals appear metallic in lustre?

Answer 99

Metals appear metallic in lustre because light does not pass through them, and this property contributes to their shiny and reflective appearance. Even thin sheets of metal, such as aluminum foil, do not allow light to pass through.

Question 100

What is the significance of hardness in mineral identification?

Answer 100

Hardness is a crucial diagnostic property in mineral identification as it determines whether a mineral can be scratched by a particular material, aiding in the classification of minerals.

Question 101

How is the Mohs Hardness Scale organized, and what does it represent?

Answer 101

The Mohs Hardness Scale is organized with 10 minerals, numbered 1 through 10 in order of increasing hardness. The scale represents a range of hardness, with each mineral on the list being harder than the one before it. However, the measured hardness is not linear on the scale.

Question 102

What are some commonly available reference materials used in the Mohs Hardness Scale, and what hardness values do they represent?

Answer 102

Some commonly available reference materials include a fingernail (2.5), copper wire (3.5), knife blade or window glass (5.5), hardened steel file (6.5), and a porcelain streak plate (7). These materials have specific hardness values and are tools used by geologists to measure the hardness of unknown minerals. If a mineral can scratch another mineral but is scratched by a specific reference material, its hardness falls within the range represented by those values on the scale. For example, if apatite is about three times harder than fluorite, and diamond is three times harder than corundum, it indicates their respective hardness relationships. *image 27

Question 103

What is crystal habit in minerals, and how is it influenced by the conditions in which minerals form?

Answer 103

Crystal habit refers to the distinctive shapes in which minerals can form crystals. It is influenced by the conditions in which minerals form within rocks. If minerals are not crowded out by pre-existing minerals, they may exhibit distinctive crystal shapes determined by their atomic structure.

Question 104

Provide examples of crystal habits and their descriptions mentioned in the text.

Answer 104

Some terms used to describe crystal habit include bladed, botryoidal (grape-like), dendritic (branched), drusy (an encrustation of crystals), equant (similar size in all dimensions), fibrous, platy, prismatic (long and thin), and stubby. *image 28

Question 105

How does the formation of crystal habits relate to the presence of other pre-existing minerals in rocks?

Answer 105

Crystal habits may not be obvious in ordinary rocks because minerals forming distinctive crystal shapes might be crowded out by other pre-existing minerals within the rocks.

Question 106

What are some examples of crystal habits for specific minerals discussed in the text?

Answer 106

Quartz forms six-sided prisms with pointed ends. Pyrite can form cubic crystals or crystals with 12 faces (dodecahedra). Garnet forms many-sided crystals with an overall rounded shape.

Question 107

Why might crystal habits be more evident in certain conditions, as mentioned in the text?

Answer 107

Crystal habits may be more evident when minerals crystallize from a hot water solution within a cavity in an existing rock, as seen in the case of quartz forming six-sided prisms with pointed ends.

Question 108

How does the atomic structure of minerals play a role in determining their crystal habits?

Answer 108

The atomic structure of minerals influences their crystal habits. Distinctive shapes are determined by how atoms are arranged in the crystal lattice, and these shapes are specific to each mineral.

Question 109

What is cleavage in minerals, and how does it differ from fracture?

Answer 109

Cleavage is the way a mineral breaks along a plane or planes, resulting in flat and smooth surfaces. Fracture, on the other hand, is an irregular break, leading to surfaces with uneven and rough textures.

Question 110

How is cleavage determined within minerals, and what does it reveal about their atomic arrangement?

Answer 110

Cleavage is determined by the arrangement of atoms within minerals, specifically the orientation of weaknesses in their crystal lattice. The way minerals break along planes provides insights into their atomic structure.

Question 111

Provide examples of minerals mentioned in the text that exhibit cleavage and fracture, and describe their characteristics.

Answer 111

Graphite and Mica: Break off in parallel sheets (*image 29). Halite: Exhibits three directions of cleavage at 90° (*image 30). Calcite: Shows three directions of cleavage not at 90° (*image 31).

Question 112

What are some challenges students may face when learning to recognize and describe cleavage?

Answer 112

1, It might be necessary to look very closely at a sample to observe mineral cleavage, as the key features can be small in scale. 2. Cleavage can be poor, meaning the cleavage surface isn't perfectly flat. 3. It can be challenging to differentiate between a cleavage plane, a crystal face, or a flat surface that isn't related to cleavage.

Question 113

Why is it important for students to practice recognizing cleavage and fracture in minerals?

Answer 113

Cleavage is a reliable diagnostic property for most minerals. Despite the challenges, practicing the recognition of cleavage and fracture helps develop the skill to identify minerals accurately.

Question 114

What is density, and how is it measured in the context of minerals?

Answer 114

Density is a measure of the mass of a mineral per unit volume. It is calculated by dividing the mass of the mineral by its volume. The formula for density is density = mass/volume.

Question 115

Why is density a useful diagnostic tool for some minerals?

Answer 115

Density is useful in identifying minerals when there is a significant variation in their densities. For example, metallic minerals like pyrite, hematite, and magnetite have densities over 5 g/cm³, making them feel much heavier compared to minerals with average density (2.6 to 3.0 g/cm³).

Question 116

Provide examples of minerals mentioned in the text that have densities over 5 g/cm³.

Answer 116

Pyrite Hematite Magnetite

Question 117

What is a limitation of using density as a diagnostic tool for minerals?

Answer 117

The limitation is that density cannot be assessed accurately in minerals that are a small part of a rock with other minerals. The presence of various minerals in a rock may hinder the accurate measurement of an individual mineral's density.

Question 118

How can calcite be identified based on its reaction with dilute acid?

Answer 118

Calcite reacts with dilute acid and will give off bubbles of carbon dioxide. This effervescence is a characteristic feature of calcite.

Question 119

What is a distinctive property of magnetite that aids in its identification?

Answer 119

Magnetite is strongly magnetic, providing a distinctive property that aids in its identification. Some other minerals are weakly magnetic.

Question 120

How can sphalerite be identified using a streak plate?

Answer 120

Sphalerite ((Zn,Fe)S) gives off a smell of sulphur when drawn across a streak plate. This olfactory characteristic is helpful in identifying sphalerite.

Question 121

How can halite be identified based on a sensory property?

Answer 121

Halite can be identified by its salty taste. This sensory property is unique to halite.

Question 122

What distinctive tactile property is associated with talc?

Answer 122

Talc feels soapy to the touch, providing a distinctive tactile property that aids in its identification

Question 123

What visual features are associated with plagioclase feldspar?

Answer 123

Plagioclase feldspar has striations (parallel razor-thin lines etched on the surface), and some varieties show a play of colors when light hits them at the right angle. An example is the labradorite in image 22