Week 2

Question 1

How is the octahedral form expressed in general form notation?

Answer 1

{111}

Question 1

A mineral aggregate composed of scales or lamellae is described as ________ when it has fine scales with divergent or featherlike structure.

A. Foliated
B. Lammelar
C. Plumose
D. Micaceous

Answer 1

C. Plumose

Question 1

What is the symbol of a form in a particular crystal class that contains faces that intersect all crystallographic axes at different lengths?

Answer 1

{hkl}

Question 1

What term is used to indicate the outward appearance of crystals in crystallography?

Answer 1

Habit

Question 2

What information does the Miller’s indices notation provide about a crystal’s form?

A. Physical properties
B. Atomic arrangement
C. Symmetry class
D. Growth conditions

Answer 2

B. Atomic arrangement

Question 3

It refers to the color of a finely powdered mineral.

Answer 3

Streak

Question 4

How many faces does a cube (isometric crystal form) have?

Answer 4

6

Question 5

It is an imaginary straight line that pass through the center of a crystal, when the crystal rotates around this axis similar face, edge or solid angle appear.

Answer 5

Axis of Symmetry

Question 6

What is the primary function of the Hermann-Mauguin notation in crystallography?

A. Describing habit
B. Identifying symmetry elements
C. Counting faces
D. Classifying chemical properties

Answer 6

B. Identifying symmetry elements

Question 7

How many faces does a tristetrahedron have?

Answer 7

12

Question 8

This is a crystal system where the unit cell is in the shape of a cube.

Answer 8

Isometric Crystal System

Question 9

This crystal system have three axes that are all equal in length and intersect at three different angles ( any angle but 90°).

Answer 9

Triclinic

Question 10

This crystal system have three axes, all at right angles, and all three of different lengths.

Answer 10

Orthorhombic

Question 11

It is a set of crystal faces that completely enclose space.

Answer 11

Closed Form

Question 12

What is the term used to describe a vesicle in a volcanic rock that is filled with secondary minerals?

Answer 12

Amygdaloidal

(e.g. calcite)

Question 13

How are open forms different from closed forms in crystallography?

Answer 13

Closed forms enclose space, open forms do not

Question 14

Differentiate malleable, ductile, and sectile.

Answer 14

Malleable - hammered into thin sheets (e.g. native copper, gold)
Ductile - drawn into thin wire (e.g. gold, silver, copper)
Sectile - cut into thin shaving with a knife (e.g. argenite)

Question 15

The crystal form - dipyramid is described as?

Answer 15

Having 6-, 8-, 12-, 16-, or 24-faced closed form in which the lower pyramid is a reflection of the upper.

Question 16

What are the characteristics of a mineral?

Answer 16

N-aturally occuring
I-norganic
D-efinite chemical composition
O-rdered crystal structure
H-omogeneous

Question 17

Define the term reniform.

Answer 17

A crystal habit described as radiating individuals terminating in round kidney-shaped masses.

(e.g. hematite)

Question 18

What is the Hermann-Mauguin notation used for?

Answer 18

Describe the point group symmetry.

Question 19

Describe the term Curie Point.

Answer 19

It is the temperature which the mineral loses its magnetism.

(Magnetite -580 deg C)
(Hematite - 680 deg C)

Question 20

What are striations?

Answer 20

These are parallel (hairline grooves) sets of linear features that appear as engraved ridges and/or grooves on mineral surfaces.

Ex. tourmaline, quartz

Question 21

In the Mohs Hardness Scale, what minerals can be scratched with fingernails?

Answer 21

Talc and Gypsum

Question 22

What is chatoyancy?

Answer 22

A play in colors that occurs specifically in fibrous minerals, when a band of light move perpendicular to fibers. (Quartz - cat's eye; tourmaline)

Question 23

Differentiate idiochromatic and allochromatic.

Answer 23

Idiochromatic - "self-colored" or its pure state or color (malachite - green) Allochromatic - "foreign-colored" due to impurities (quartz)

Question 24

What is the primary characteristic of a pyramid in crystallography?

Answer 24

Faces meeting in a point

Question 25

The closed crystal form - rhombohedron is described to have?

Answer 25

6 identical faces with none of the intersection edges perpendicular

Question 26

What is a form in crystallography?

Answer 26

A group of crystal faces with the same relationship to symmetry

Question 27

Differentiate pedion and pinacoid.

Answer 27

Pedion (Monohedron) - singe face Pinacoid (Parallelohedron) - 2 parallel faces

Question 28

Differentiate the 3 basic types of magnetism.

Answer 28

Ferromagnetism - strong magnetism Paramagnetism - weak attraction, but most are strongly magnetic when heated Diamagnetism - repelled from magnetic fields

Question 28

Globular is simply defined as:

Answer 28

radiating individuals forming spherical or hemispherical groups

Question 29

What is a mineraloid?

Answer 29

A mineraloid is a mineral -like substance that does not demonstrate crystallinity. (e.g. glass, opal, obsidian)

Question 30

What is a 2-fold rotation axis?

Answer 30

If an object appears identical after a rotation of 180 deg, that is twice in a 360 deg rotation, then it is said to have a 2-fold rotation axis.

Question 31

Expound open crystal form and give an example.

Answer 31

Open forms do not enclose space. Examples: Pedion, prism, pinacoid, domes, pyramid

Question 32

What are the geochemical affinities in the Goldschmidt Classification?

Answer 32

Lithophile - silicate (aluminum, boron) Siderophile - iron (iridium, gold) Chalcophile - sulfur (Copper, Sulfur) Atmophile - gas (Helium, hydrogen)

Question 33

Which of the following are different from the other and why? A. Sphenoids B. Disphenoids C. Pinacoids D. Prism

Answer 33

A. Sphenoids - open form (mura atop) B. Disphenoids - closed form (mura pyramid; 4 faces) C. Pinacoids - open form (2 parallel faces) D. Prisms - open form (3 or more parallel faces)

Question 34

Why is pedion an open crystal form?

Answer 34

Pedions are single faced forms. Since there is only one face in the form a pedion cannot completely enclose space. Thus, a crystal that has only pedions, must have at least 3 different pedions to completely enclose space.

Question 35

Expound the characteristics of the isometric crystal system (emphasizing symmetry elements) and provide examples.

Answer 35

Expound the characteristics of the isometric crystal system (emphasizing symmetry elements) and provide examples.

Question 36

Explain the concept of a crystal system and provide an example of a mineral for each of the six crystal systems.

Answer 36

The crystal system defines the geometric arrangement of crystal classes. Examples: Isometric (Cubic) - Pyrite Hexagonal - Quartz Tetragonal - Rutile Orthorhombic - Topaz Monoclinic - Azurite Triclinic - Anorthite

Question 37

Explain the features of a prism crystal form. and a pyramid crystal form. Provide examples of minerals with prismatic and pyramidal crystal habits.

Answer 37

Prism has parallel faces; pyramid has faces intersecting at a point. Examples: Monoclinic Prism - Augite; Tetragonal Pyramid - Rutile.

Question 38

What is the main reason why quartz have so many varieties?

Answer 38

Due to the different formation environments. Because of the different temperatures and pressure during the formation, different impurities can get into the quartz structure.

Question 39

Although objects themselves may appear to have 5-fold, 7-fold, 8-fold, or higher-fold rotation axes, these are not possible in crystals. Explain why.

Answer 39

The reason is that the external shape of a crystal is based on a geometric arrangement of atoms. Note that if we try to combine objects with 5-fold and 8-fold apparent symmetry, they do not completely fill space as illustrated.

Question 40

Illustrate the silicate structure of (Mg,Fe)2SiO4.

Question 41

Illustrate the cleavage exhibited by pyroxenes.

Answer 41

two distinctive planes of cleavage with intersecting angles of about 87° and 93°

Question 42

Which of the following is different and why? A. Deltoid dodecahedron B. Tetrahexahedron C. Hexagonal scalenohedron D. Hextetrahedron

Answer 42

A. Deltoid dodecahedron - Isometric B. Tetrahexahedron - Isometric C. Hexagonal scalenohedron - Non-isometric D. Hextetrahedron - Isometric

Question 43

Which of the following is true about a mineral? Provide a short explanation of each item. A. It can be produced in a laboratory. B. A solid substance that can be physically subdivided into simpler chemical compounds. C. The atoms or groups of atoms must occur in specific ratios. D. Includes compounds that contain carbon.

Answer 43

A. It can be produced in a laboratory. - must be naturally occuring B. A solid substance that can be physically subdivided into simpler chemical compounds. - homogeneous means cannot be physically subdivided C. The atoms or groups of atoms must occur in specific ratios. - means it has definite chemical composition D. Includes compounds that contain carbon - inorganic means no carbon

Question 44

Give one variety of garnet and provide its composition and occurence.

Question 45

Give one variety of macroscopic quartz and provide its color and cause of color.

Question 46

Provide a mineral that have a greasy feel? Discuss how this occurred.

Answer 46

Minerals such as talc, graphite, and molybdenite possess a greasy feel. This results from weak van der waals bonds that allow the minerals to be broken into soft, dust-like fragments that "lubricate" the surface when the specimen is rubbed with the fingers.