Identification of Minerals Flashcards
The following properties can be observed at what light?
Opacity, Relief, Habit, form, Mode of Aggregation, Relative Index of Refraction, Color, Pleochroism, Habit, Form, Cleavage
Plane polarized Light (PPL)
The following properties can be observed at what light?
Isotropic vs Anisotropic, Habit, Form, Mode of Aggregation, Cleavage, Interference Color, Sign of Elongation, Extinction and Extinction Angles, Twinning, Zoning
Cross Polarized Light (XPL)
The function of the wavelength transmitted by the mineral.
Color
The _______ of a mineral in hand specimen
and in thin section have the same hue although
the _______ in thin section is typically not as intense
Color
The ability of a mineral to absorb different wavelengths of transmitted light depending upon its crystallographic orientation
Pleochroism
Pleochroism is used to describe the color variation for __________ __________ with the polarization direction of the light, which depends on the orientation of the material in the light path
Destructive Interference
Colored _________ and _________ are usually pleochroic.
Uniaxial, Biaxial
Term for pleochroic hexagonal, trigonal, and tetragonal minerals.
Twofold Pleochroism
Other term for twofold pleochroism.
Dichroism
Term for pleochroic orthorhombic, monoclinic and triclinic
minerals
Trichroic
Light vibrating at Optic Axis = color 1; light at perpendicular to Optic Axis = color 2
Uniaxial Minerals
Minerals that exhibit varying degrees of absorption
Biaxial Minerals
Pleochroism described as darkest at long axis oriented perpendicular to polarizer
Normal Pleochroism
Type of pleochroism described as darkest at long axis oriented parallel to polarizer
Reverse Pleochroism
The degree to which mineral grains stand out from the mounting medium.
Have sharp grain boundaries, show fractures and cleavages well.
Relief
Property of a mineral that describes its shape/appearance.
Habit / Form
Without regular crystal faces.
Anhedral
Has well-formed crystal faces.
Euhedral
Has crystal faces but they are poorly formed or irregular.
Subhedral
Elongated, needle-like grains.
Acicular
Elongated and Slender.
Bladed
Shaped like a column; moderately elongated grains with equidimensional cross section.
Columnar
Equidimensional Grains.
Equant
Individual grains are long slender fibers.
Fibrous
Flat, elongated grains.
Lathlike
The dominant faces are those of a prism.
Prismatic
Shaped like a book.
Tabular
Refers to how the individual mineral grains are grouped together to form a larger structure or assemblage.
Mode of Aggregation
Parallel arrangement of columnar grains.
Columnar
More or less parallel, tabular, or platy grains; flaky.
Foliated
Equant grains, all about the same size.
Granular
Elongated grains in a random pattern.
Matted
Elongated grains that radiate out from a center.
Radiating
The way a mineral splits in preferred directions.
Represents the planes of weak bonding in the mineral’s atomic structure.
Cleavage
A mineral’s cleavage should be repetitive and subparallel. If this circumstaces are not met, the mineral has a ________ instead of a cleavage.
Fracture
Characterizations of mineral cleavages.
Perfect, Good, and Weak/Poor
Light rays are parallel to the wave normal.
Shows the same velocity of light in all directions.
Bonds are the same in all directions.
Isotropic Materials
Example of isotropic materials.
Isometric Minerals and Mineraloids
Light rays are not parallel to the wave normal.
Shows difference velocities of light in all directions.
Bonds are not the same in all directions.
Anisotropic Materials
Example of Anisotropic Materials
Tetragonal, Trigonal, Hexagonal, Orthorhombic, Monoclinic, and Triclinic Minerals
The wavelength (color) exhibited by a mineral
when viewed under XPL.
Interference Color
Resultant of two superimposed polarized light emerging from analyzer.
Interference Colors
Maximum interference colors can be observed ______ degrees from the extinction position.
45
Chart used to assign interference colors.
Michel-Levy Color Chart
Observed under XPL, dependent on orientation of mineral, or presence of cleavages of mineral grain.
Extinction
Types of Extinxtions on Minerals
Parallel, Symmetrical, Inclined, Undulose
All uniaxial minerals exhibit ______ extinction.
— the crystal axes and indicatrix axes coincide.
Parallel
Orthorhombic minerals show ________ extinction.
Parallel
Monoclinic and triclinic minerals have ________
extinctions.
— indicatrix axes do not coincide with crystallographic axes.
— extinction angle helps to further identify them.
Inclined
No cleavage to base extinction from.
No Extinction Angle
Different parts of a grain become extinct at different angles.
— consequence of stress, deformation
Undulose / Undulatory Extinction
The distance that one wave lags behind the other (measured in nm).
Retardation
Where i is an integer, then the two waves are said to be in phase.
Constructive Interference
Two waves are said to be out of phase.
Destructive Interference
True or False
Light rays travelling along the same path will the same direction will not interfere with each other.
False, they will interfere with each other.
A property used to determine which of the two rays coming through the mineral is the slow ray and which is the fast ray.
When these two rays leave the top of the mineral grain, the slow ray is behind the fast ray by a distance equal to the retardation Δ1.
Sign of Elongation
What is produced when a material with known retardation ΔA is superimposed over the mineral so that the slow ray vibration directions are parallel, the resulting slow ray and is further retarded.
Higher Interference Colors
What is produced when a mineral’s fast ray is parallel to the slow ray of the material with known retardation ΔA, slow ray of mineral becomes fast ray in material with known retardation ΔA; mineral’s fast ray is retarded.
Lower Interference Colors
When looking for signs of elongation, when the interference color of a mineral increases, it can be characterized as _________.
Length-slow
When looking for signs of elongation, when the interference color of a mineral decreases, it can be characterized as _________.
Length-fast
Three types of compensators/accesory plates/retardation plates.
Muscovite/Mica, Gypsum, and Quartz Plates
The compensator marked with 137 nanometers.
Muscovite / Mica Plate
The compensator marked with 500 nanometers.
Gypsum Plate
Fast ray direction.
NW-SE
Slow ray direction.
NE-SW
Other term for length-slow sign of elongation.
Positive Elongation
Other term for length-fast sign of elongation.
Negative Elongation
When looking for signs od elongation, if the mineral has 1 degree white-gray interference color, ______ plate should be used.
Mica
When looking for signs of elongation, color blind users shall use the _______ ________.
Quartz Wedge
The intergrowth of two or more crystals in a
symmetrical fashion by the sharing of lattice
points in adjacent crystals.
—best observed in plagioclase, but other minerals
such as quartz, pyrite, fluorite, etc.
Twinning
Type of twinning observed in Albites, where in hand samples it can be observed as striations, and in thin sections can be observed as inter-layering of colors.
Albite Twinning
The most common type of twinning observed in orthoclase.
Carlsbad Twinning
_________ twinning only occurs in Triclinic feldspars.
Albite
_________ twinning occurs in monoclinic and triclinic fledspars.
Carlsbad
__________ twinning is a characteristic feature of the mineral Microcline, defined as the combination of albite and pericline twinning laws.
Tartan
Variation in the extinction angle from one zone to another.
Albite-Anorthite Series
Common, particularly in volcanic and hypabyssal intrusive rocks.
Zoning
Changes smoothly from a more calcic core to a more sodic rim.
Core has a larger extinction angle.
Normal Zoning
Changes smoothly from a more sodic core to a more calcic rim.
Core has a smaller extinction angle.
Reverse Zoning
Alternation between calcic and sodic zones.
Usually from a more calcic core to a more
sodic rim.
Oscillatory Zoning
A _______ zoned plagioclase has a calcic core and sodic rim.
Normal
The higher the Calcium content, the _________ the extinction angle of plagioclase.
Higher
1λ of the compensator corresponds to ________ nanometers.
500
Biaxial minerals exhibit ________ pleochroic colors.
Varying
True or False:
A euhedral mineral has no regular crystal faces.
False, euhedral minerals has well-developed crystal faces.
