Week2 D2

Question 1

Study of crystal bodies and the laws that dictate parameters such as growth, shape and geometry

Answer 1

Crystallography

Question 2

A term that denotes the ordered arrangement of atoms in an object’s structure

Answer 2

Crystalline

Question 3

Subtances with microscopic level of crystalinity

Answer 3

Cryptocrystalline

Question 4

Those without any crystalline structure

Answer 4

Amorphous

Question 5

minute particles that are arranged in a 3D pattern that keeps repeating almost indefinitely

Answer 5

lattice

Question 6

A powerful method in determining the structural constrains of minerals. It utilizes monochromatic radiation and that is beamed on a crystal rotated about its major axis

Answer 6

Rotation method

Question 7

Smooth planar surfaces resulting from cleavage breaks.

Answer 7

Cleavage planes

Question 8

An instrument used to measure interfacial crystal angles

Answer 8

Goniometers

Question 9

Considered to be a guarantee of the chemical homogeneity of a mineral
A. Crystal B. Color C. Streak D. Chemical composition

Answer 9

A. Crystal

Question 10

Classification of crystal classes/systems is based mainly on

Answer 10

symmetry

Question 11

crystal is said to have a ___ if an imaginary line can be passed from any point on its surface through its center and a similar point is found on the line at an equal distance beyond the center.

Answer 11

Center of Symmetry

Question 12

How many crysal classes are possible

Answer 12

32

Question 13

Symmetry of a Hexoctahedral crystal class

Answer 13

C, 3A4, 4A3, 6A2, 9P

Question 14

Symmetry of a Dihexagonal-Dipyramidal crystal class

Answer 14

C, 1A6, 6A2, 7P

Question 15

The only crystal class with not symmetry

Answer 15

Pedial

Question 16

Definition of a mineral

Answer 16

A mineral is an object that is naturally occuring, stable at room temperature, formed by inorganic process, represented by a chemical formula, and has an ordered atomic arrangement

Question 17

Three prominent modes of crystallization

Answer 17

Solution, Fusion, Vapor

Question 18

What is a unit cell

Answer 18

smallest portion of a crystal that still exhbit its properties

Question 19

What is X-ray diffraction

Answer 19

The patterned interference of incident x-ray beams when passing through a crystal due to their uniform spacing.

Question 20

Briefly explain the Laue photograph

Answer 20

A photographic record that shows the pattern of xray beams that diffracts when passing through a mineral. The dark spots indicate the positoins of the crystal lattice and the arrangement is a manifestation of a crystal’s symmetry.

Question 21

Define cleavage

Answer 21

Tendency of a crystal to split into perfect planes due to inherent weaknesses in a crystal lattice

Question 22

The outward form of a mineral depends on what factors?

Answer 22

The unit shape and the environment in which they are formed

Question 23

External influences found in a mineral’s environment include

Answer 23

temperature, pressure, nature of solution, speed of crystal growth, surface tension, and direction of the movement of the solution.

Question 24

Face positions of a crystal is dependent on

Answer 24

which direction through the internal structure that has the greatest number of crystal units

Question 25

Fundamental symmetry operations

Answer 25

1. Rotation about an axis 2. reflection in a plane 3. combined rotation and reflection

Question 26

Define symmetry plane

Answer 26

imaginary plane which divides a crystal into halves, each of which, in a perfectly developed crystal, is the mirror image of the other.

Question 27

Define symmetry axis

Answer 27

an imaginary line through a crystal about which the crystal may be revolved and repeat itself in appearance two or more times during a complete revolution.

Question 28

What is a binary symmetry.

Answer 28

A crystal is repeated twice in appearance during a complete revolution

Question 29

What are the possible axes that a crystal can manifest

Answer 29

2-, 3-, 4-, and 6- fold axes

Question 30

What would be the symmetry notation of a crystal with a center, 3 two fold symmetry, four 3 fold symmetry, and 3 planes

Answer 30

C, 3A2, 4A3, 3P

Question 31

Crystal classes belonging to Monoclinic

Answer 31

Prismatic, Spheroidal, Domatic

Question 32

Crystal classes belonging to Triclinic

Answer 32

Pinacoidal, Pedial

Question 33

Enumerate the six crystal systems

Answer 33

Isometric, hexagonal, tetragonal, orthohombic, monoclinic, triclinic

Question 34

Describe the isometric system

Answer 34

has three mutually perpendicular axes with same lengths

Question 35

Describe the hexagonal system

Answer 35

has 4 axes, three equal horizontal axes intersect at 60 degrees, fourth axes has different length and intersects perpendicular to the other three axes

Question 36

How does a solution based crystallization happen and give examples?

Answer 36

A brine solution (common salt + water) becomes supersaturated where it comes to a point that no solute can be held and salt must be precipirated. Under the right conditions (slow evaporation of water), salt separates from water and crystals will eventurally form.

Question 37

How does temp and pressure relate to crystallization?

Answer 37

Lowering temperature and/or pressure can result in the formation of crystals. Solutions with higher PT conditions can slightly dissolve more. Lowering those conditions would lower its capacity and thus making it supersaturated enough to encourage crystal formation.

Question 38

How does a fusion based crystallization happen and give examples?

Answer 38

A change in temperature would cause atoms to be fixed in their position and arrange themselved in order to build a crystalline mass. Ice for example is fused water then temperatures drop. Similarly, magmas fused into crystalline masses under certain temperatures.

Question 39

How does a vapor based crystallization happen and give examples?

Answer 39

A solid with a crystal structure is formed from the cooling of gas. The formation of sulfur crystals from fumaroles is an example.

Question 40

Can a unit cell be small as an atom?

Answer 40

No. The interrelation of atoms are an important aspect in determining the properties of a specific substance and so a subdivision smaller than the unit cell wouldn’t have the properties of a mineral. Thus, a Na and a Cl atom separately has different properties when compared to the mineral Halite (NaCl)

Question 41

How is Xray diffraction relevant in a crystallography

Answer 41

X ray diffraction results when the gaps in the atomic structure filters x-rays in such a way that geometrical patterns can be seen when they fall on a photographic plate. Such patterns are used in studying the internal strucutre of crystals

Question 42

In a nutshell, what are the steps involved in the powdered method.

Answer 42

The powdered method is another way of analysing the internal structure of a crystal. In this manner, the sample is grinded into a powder and is then subjected to x-ray beam. Diffracted radiation is recorded on a film in which the structure can be calculated.

Question 43

Describe the cleavage of halite, relate it to its crystal structure

Answer 43

Cleaves well on three planes at right angles to each other. Cleavages are always parallel to the external facets of the crytal strucutre.

Question 44

Glass does not produce optical properties (such as double refraction) in contrast to other similarly transparent objects such as calcite. Why is this the case?

Answer 44

Glass lacks the definite internal structure that can distort light passing through unlike calcite.

Question 45

Why is it that flourite can exhibit cubic and octahedral crystal habits even if the building blocks have the same internal structure?

Answer 45

A difference in the external factors of a mineral’s environment is a cause of the variations growth rates in different directions. Thus making the external expressions different despite having the same internal structure.

Question 46

Explain and Illustrate the Law of the constancy of interfacial angles

Answer 46

The law states that the angles are the same in corresponding faces on crystals of the same substance.

Question 47

Explain and Illustrate the Axis of rotary Reflection

Answer 47

combines a rotation about an axis with reflection across a plane at right angles to the axis.

Question 48

Explain the dual nature of light

Answer 48

Light can be described as both a particle and a wave. Light as explained in the particle theory is composed of subatomic particles called photons which are produced when valence electrons of an excited ion relases energy. The wave theory meanwhile described light as a transverse wave that has elctrical and magnetic properties.

Question 49

Why is the electric vector of the EM wave important in optical mineralogy.

Answer 49

The interaction between the electric vector and the electrical character of atoms and chemical bonds of a mineral greatly affects the behviour of light. These behaviour is extensively studied in optical mineralogy.

Question 50

Describe and Illustrate the light wave.

Answer 50

A lightwave can be mathematically described as f=V/lamda where f is frequecy, V is velocity and lamda is the wavelength. The velocity of light is a constant, so if f changes, so does V.