4.Crystallography of Gem Minerals

Welcome to your Module 4 - Crystallography of Gem Minerals

What is crystallography?

a) Study of crystals and their structures

b) Study of fossils

c) Study of plant cells

d) Study of insects

2. Which mineral is known for its perfect octahedral crystals?

a) Quartz

b) Diamond

c) Calcite

d) Corundum

3. What is the primary method used to study the internal structure of gem minerals?

a) Scanning electron microscopy

b) X-ray diffraction

c) UV-Vis spectroscopy

d) Nuclear magnetic resonance

4. Name a gemstone that crystallizes in the hexagonal system.

a) Ruby

b) Emerald

c) Sapphire

d) Diamond

5. How does crystal habit affect the appearance of a gemstone?

a) It determines the color

b) It affects the luster

c) It influences the overall shape

d) It changes the hardness

6. Define a crystal in terms of its atomic structure.

a) A solid with a random atomic arrangement

b) A solid with a well-ordered atomic structure

c) A solid with liquid-like properties

d) A solid that conducts electricity

7. What is the difference between a crystal and a glass?

a) Crystals are transparent, glasses are not

b) Crystals have ordered atomic structures, glasses do not

c) Glasses are natural, crystals are synthetic

d) Glasses have higher melting points than crystals

8. What is the significance of the unit cell in a crystal?

a) It is the smallest repeating unit of the crystal lattice

b) It determines the color of the crystal

c) It is the largest component of the crystal

d) It dictates the crystal's weight

9. Describe the term "anisotropy" in the context of crystals.

a) Property of being the same in all directions

b) Property of being different in different directions

c) Ability to conduct electricity

d) Ability to reflect light

10. Why are crystals often studied using X-ray diffraction?

a) To determine their color

b) To find their atomic structure

c) To measure their hardness

d) To assess their weight

11. What distinguishes a polycrystalline material from a single crystal?

Crystals, Polycrystals, and Amorphous

a) Polycrystalline materials are larger

b) Single crystals are more common

c) Polycrystalline materials consist of many small crystals

d) Single crystals have more defects

12. Give an example of an amorphous solid.

a) Quartz

b) Glass

c) Diamond

d) Graphite

13. How does the structure of polycrystalline materials affect their properties?

a) Makes them less transparent

b) Makes them more brittle

c) Results in isotropic properties

d) Creates different mechanical properties

14. What is a grain boundary in a polycrystal?

a) The outer surface of a crystal

b) The interface between two crystals

c) The center of a crystal

d) The color change in a crystal

15. How does cooling rate affect the formation of crystals versus amorphous solids?

a) Slow cooling favors amorphous solids

b) Fast cooling favors crystal formation

c) Slow cooling favors crystal formation

d) Cooling rate has no effect

16. How many crystal systems are there?

Crystal Systems

a) 4

b) 5

c) 6

d) 7

17. Which crystal system has all axes of equal length and all angles equal to 90 degrees?

a) Hexagonal

b) Cubic

c) Tetragonal

d) Monoclinic

18. What are the defining characteristics of the tetragonal crystal system?

a) Two axes of equal length, one different, and all angles 90 degrees

b) All axes different lengths and all angles 90 degrees

c) All axes equal and all angles 120 degrees

d) One axis different length and angles not 90 degrees

19. Name a mineral that belongs to the monoclinic crystal system.

a) Quartz

b) Feldspar

c) Diamond

d) Corundum

20. Which crystal system includes the cubic system as a subset?

a) Triclinic

b) Monoclinic

c) Orthorhombic

d) Tetragonal

21. What is meant by crystal symmetry?

Crystal Symmetry

a) Uniform color throughout the crystal

b) Ordered arrangement of atoms in the crystal

c) Repetition of a pattern at regular intervals

d) External shape of the crystal

22. Define a symmetry element in crystallography.

a) A point, line, or plane about which symmetry is observed

b) The color of the crystal

c) The weight of the crystal

23. What is a mirror plane in the context of crystal symmetry?

a) A plane that divides a crystal into two identical halves

b) A line around which a crystal rotates

c) A point in the center of a crystal

d) A surface that reflects light

24. How does rotational symmetry differ from translational symmetry?

a) Rotational symmetry involves repetition through translation

b) Rotational symmetry involves repetition through rotation

c) Translational symmetry involves rotation of the crystal

d) Translational symmetry does not exist in crystals

25. What is a crystallographic point group?

a) A classification of crystals based on their external form

b) A group of atoms in a crystal

c) A set of symmetry operations that leave at least one point unmoved

d) A collection of crystals with the same color

26. What is crystal habit?

Crystal Habits and Forms

a) The color of the crystal

b) The typical external shape of a crystal

c) The internal structure of a crystal

d) The chemical composition of a crystal

27. Describe the tabular habit of crystals.

a) Crystals that form in thin plates

b) Crystals that form in long, slender rods

c) Crystals that form in cube shapes

d) Crystals that form in spherical shapes

28. How does environmental growth conditions influence crystal habit?

a) They determine the color

b) They have no effect

c) They affect the size and shape of crystals

d) They change the chemical composition

29. What is the difference between a crystal form and a crystal habit?

a) Form is internal structure; habit is external appearance

b) Form is chemical composition; habit is internal structure

c) Form is external appearance; habit is internal structure

d) Form and habit are the same

30. Name a crystal habit that is typical for quartz.

a) Cubic

b) Acicular

c) Prismatic

d) Botryoidal

31. What is a twinned crystal?

Twinning of Crystals

a) A crystal with two identical faces

b) Two crystals that grow together in a symmetrical manner

c) A crystal with double the number of atoms

d) A crystal that splits into two

32. Describe the difference between contact twinning and penetration twinning.

a) Contact twinning forms parallel lines; penetration twinning forms angles

b) Contact twinning forms at crystal faces; penetration twinning interpenetrates

c) Contact twinning occurs in nature; penetration twinning is synthetic

d) Contact twinning involves two crystals; penetration twinning involves one

33. What causes twinning in crystals?

a) Impurities in the crystal

b) External stress and growth conditions

c) Excessive heat

d) Chemical reactions

34. Name a mineral commonly found in twinned form.

a) Quartz

b) Feldspar

c) Diamond

d) Corundum

35. What is a twin plane in crystallography?

a) The boundary where twinning occurs

b) A surface that splits the crystal

c) A plane where two crystals meet

d) The top surface of a crystal

36. What are crystal faces?

Surface Features of Crystals

a) The color of a crystal

b) Flat surfaces on a crystal

c) The internal planes of a crystal

d) The points of a crystal

37. Define the term "facet" as used in gemology.

a) A type of crystal defect

b) A flat polished surface on a gemstone

c) The internal structure of a crystal

d) A natural surface on a mineral

38. What is the significance of cleavage planes in minerals?

a) They determine the mineral's color

b) They are the planes along which a mineral breaks easily

c) They affect the mineral's weight

d) They determine the hardness

39. Describe the term "striations" on crystal surfaces.

a) Parallel lines on the surface of a crystal

b) Irregular cracks on the surface

c) Small pits on the surface

d) Colored bands on the surface

40. What is meant by "etch pits" on crystal surfaces?

a) Tiny depressions formed by chemical attack

b) Scratches formed by abrasion

c) Small bumps on the surface

d) Natural grooves on the surface

41. What is the Miller index notation used for?

Miller Index

a) Identifying the weight of crystals

b) Classifying the color of crystals

c) Describing crystal planes

d) Measuring the hardness of crystals

42. How do you determine the Miller indices of a crystal face?

a) By measuring the angles between planes

b) By counting the atoms on the plane

c) By finding the intercepts of the plane with the crystal axes

d) By observing the color of the plane

43. Explain what the Miller indices (1 0 0) represent.

a) A plane parallel to the y-axis

b) A plane intersecting the x-axis

c) A plane intersecting the z-axis

d) A plane parallel to the x-axis

44. What does a negative Miller index indicate?

a) The plane is not in the crystal

b) The plane is in the negative direction of the axis

c) The plane is curved

d) The plane is perpendicular to the axis

45. How are Miller indices used to identify crystal faces?

a) By measuring the angles between faces

b) By describing the orientation of the face relative to the crystal axes

c) By determining the size of the face

d) By identifying the color of the face

46. Give an example of Miller indices for a plane parallel to the x-axis.

a) (1 0 0)

b) (0 1 0)

c) (0 0 1)

d) (1 1 1)

47. What is the relationship between the Miller indices and the crystallographic axes?

a) Miller indices describe the angles between axes

b) Miller indices indicate the intercepts with the axes

c) Miller indices measure the distance between planes

d) Miller indices define the color of the crystal

48. How are Miller indices helpful in identifying cleavage planes?

a) They describe the crystal's color

b) They indicate the planes along which the crystal will break

c) They measure the crystal's hardness

d) They define the crystal's weight

49. What does the Miller index (0 1 1) represent in terms of intercepts?

a) The plane intercepts the y and z axes but not the x axis

b) The plane is parallel to the y and z axes

c) The plane intercepts the x and y axes but not the z axis

d) The plane is parallel to the x and y axes

50. How can Miller indices be used to describe the orientation of a crystal plane?

a) By identifying the color of the plane

b) By measuring the size of the plane

c) By indicating the angles between the plane and the crystal axes

d) By describing the intercepts of the plane with the crystal axes

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