Week 2 Flashcards
How is the octahedral form expressed in general form notation?
{111}
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
C. Plumose
What is the symbol of a form in a particular crystal class that contains faces that intersect all crystallographic axes at different lengths?
{hkl}
What term is used to indicate the outward appearance of crystals in crystallography?
Habit
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
B. Atomic arrangement
It refers to the color of a finely powdered mineral.
Streak
How many faces does a cube (isometric crystal form) have?
6
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.
Axis of Symmetry
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
B. Identifying symmetry elements
How many faces does a tristetrahedron have?
12
This is a crystal system where the unit cell is in the shape of a cube.
Isometric Crystal System
This crystal system have three axes that are all equal in length and intersect at three different angles ( any angle but 90°).
Triclinic
This crystal system have three axes, all at right angles, and all three of different lengths.
Orthorhombic
It is a set of crystal faces that completely enclose space.
Closed Form
What is the term used to describe a vesicle in a volcanic rock that is filled with secondary minerals?
Amygdaloidal
(e.g. calcite)
How are open forms different from closed forms in crystallography?
Closed forms enclose space, open forms do not
Differentiate malleable, ductile, and sectile.
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)
The crystal form - dipyramid is described as?
Having 6-, 8-, 12-, 16-, or 24-faced closed form in which the lower pyramid is a reflection of the upper.
What are the characteristics of a mineral?
N-aturally occuring
I-norganic
D-efinite chemical composition
O-rdered crystal structure
H-omogeneous
Define the term reniform.
A crystal habit described as radiating individuals terminating in round kidney-shaped masses.
(e.g. hematite)
What is the Hermann-Mauguin notation used for?
Describe the point group symmetry.
Describe the term Curie Point.
It is the temperature which the mineral loses its magnetism.
(Magnetite -580 deg C)
(Hematite - 680 deg C)
What are striations?
These are parallel (hairline grooves) sets of linear features that appear as engraved ridges and/or grooves on mineral surfaces.
Ex. tourmaline, quartz
In the Mohs Hardness Scale, what minerals can be scratched with fingernails?
Talc and Gypsum
What is chatoyancy?
A play in colors that occurs specifically in fibrous minerals, when a band of light move perpendicular to fibers. (Quartz - cat’s eye; tourmaline)
Differentiate idiochromatic and allochromatic.
Idiochromatic - “self-colored” or its pure state or color (malachite - green)
Allochromatic - “foreign-colored” due to impurities (quartz)
What is the primary characteristic of a pyramid in crystallography?
Faces meeting in a point
The closed crystal form - rhombohedron is described to have?
6 identical faces with none of the intersection edges perpendicular
What is a form in crystallography?
A group of crystal faces with the same relationship to symmetry
Differentiate pedion and pinacoid.
Pedion (Monohedron) - singe face
Pinacoid (Parallelohedron) - 2 parallel faces
Differentiate the 3 basic types of magnetism.
Ferromagnetism - strong magnetism
Paramagnetism - weak attraction, but most are strongly magnetic when heated
Diamagnetism - repelled from magnetic fields
Globular is simply defined as:
radiating individuals forming spherical or hemispherical groups
What is a mineraloid?
A mineraloid is a mineral -like substance that does not demonstrate crystallinity. (e.g. glass, opal, obsidian)
What is a 2-fold rotation axis?
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.
Expound open crystal form and give an example.
Open forms do not enclose space. Examples: Pedion, prism, pinacoid, domes, pyramid
What are the geochemical affinities in the Goldschmidt Classification?
Lithophile - silicate (aluminum, boron)
Siderophile - iron (iridium, gold)
Chalcophile - sulfur (Copper, Sulfur)
Atmophile - gas (Helium, hydrogen)
Which of the following are different from the other and why?
A. Sphenoids
B. Disphenoids
C. Pinacoids
D. Prism
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)
Why is pedion an open crystal form?
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.
Expound the characteristics of the isometric crystal system (emphasizing symmetry elements) and provide examples.
Expound the characteristics of the isometric crystal system (emphasizing symmetry elements) and provide examples.
Explain the concept of a crystal system and provide an example of a mineral for each of the six crystal systems.
The crystal system defines the geometric arrangement of crystal classes.
Examples:
Isometric (Cubic) - Pyrite
Hexagonal - Quartz
Tetragonal - Rutile
Orthorhombic - Topaz
Monoclinic - Azurite
Triclinic - Anorthite
Explain the features of a prism crystal form. and a pyramid crystal form.
Provide examples of minerals with prismatic and pyramidal crystal habits.
Prism has parallel faces; pyramid has faces intersecting at a point. Examples: Monoclinic Prism - Augite; Tetragonal Pyramid - Rutile.
What is the main reason why quartz have so many varieties?
Due to the different formation environments. Because of the different temperatures and pressure during the formation, different impurities can get into the quartz structure.
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.
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.
Illustrate the silicate structure of (Mg,Fe)2SiO4.
Illustrate the cleavage exhibited by pyroxenes.
two distinctive planes of cleavage with intersecting angles of about 87° and 93°
Which of the following is different and why?
A. Deltoid dodecahedron
B. Tetrahexahedron
C. Hexagonal scalenohedron
D. Hextetrahedron
A. Deltoid dodecahedron - Isometric
B. Tetrahexahedron - Isometric
C. Hexagonal scalenohedron - Non-isometric
D. Hextetrahedron - Isometric
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.
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
Give one variety of garnet and provide its composition and occurence.
Give one variety of macroscopic quartz and provide its color and cause of color.
Provide a mineral that have a greasy feel? Discuss how this occurred.
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.
