Optical Mineralogy Flashcards
_______ minerals will transmit light.
Transparent
_________ minerals block light from passing through them
opaque
T or F. Minerals that are darkly colored in hand sample will also appear to have color in thin section
T
_______ when a mineral changes color as it is rotated relative to the polarizer in plane polarized light
Pleochroism
_________ of a mineral characterizes the relationship between the speed of light in a vacuum and the speed of light in that material.
refractive index
Refractive index of kyanite ranges from ______.
1.712-1.734
Mineral _______ is related to the refractive index of the mineral. If a mineral has a refractive index that is much higher or lower than the surrounding materials, it will stand out relative to the surrounding material and will have thick or distinct .
relief
Refractive index > 0.12 different from surrounding media
High relief
Refractive index 0.04 – 0.12 different from surrounding media
Intermediate relief
Refractive index <0.04 different from surrounding media
Low relief
The relative refractive indices of two materials (minerals, glass, or epoxy) adjacent to each other in a thin section can be determined using ______.
Becke lines
Refers to the ideal crystal form, or the shape a mineral takes when left to grow without barriers or interference with other nearby mineral grains.
Mineral Form
Minerals show perfect or nearly perfect crystal faces
Euhedral
Minerals are rounded but still show the general characteristic shape of that mineral
Subhedral
Crystals are completely irregular in shape and do not resemble the characteristic form for that mineral.
Anhedral
The tendency of minerals to break along atomic planes of weakness within the crystal structure
Cleavage
Irregular cracks within a mineral. These can form within any mineral, but when only fractures appear in a mineral, it may indicate that it has poor or no cleavage.
Fractures
__________ minerals have crystal structures which have the same structure in every direction.
Isotropic
Isotropic minerals belong ____________ system.
Isometric
_________ crystal structures vary with direction.
Anisotropic
Anisotropic minerals belong to ____________.
hexagonal, tetragonal, orthorhombic, monoclinic, and triclinic crystal systems
PPL - Mineral appears dark
XPL - Mineral appears dark even when rotated
Opaque
PPL - Light passes through mineral
XPL - Mineral appears dark even when rotated
Isotropic
PPL - Light passes through mineral
XPL - Mineral exhibits interference colors and goes dark (extinct) every 90 degrees
Anisotropic
A mineral with _________ will go extinct with the cleavage at an angle to these directions as the stage is rotated.
inclined extinction
A mineral with __________ will go extinct (dark) when the cleavage direction is parallel to the north-south and east-west directions as the stage is rotated.
parallel extinction
The color of a mineral under cross-polarized light is called its _____________
interference color
Interference colors categorized by _____________________ order colors
first, second, third, and fourth
This diagram displays the interference colors in the chart, with verbal descriptions of first-, second-, and third-order colors below the x-axis. The y-axis on the left side of the diagram is thickness of the mineral (or thin section) in micrometers.
Michel-Levy Interference Color Chart
______________ the phenomenon exhibited by certain materials in which an incident ray of light is split into two rays, called an ordinary ray and an extraordinary ray, which are plane-(linear) polarized in mutually orthogonal planes, or circular-polarized in opposite directions (left and right).
Birefringence (δn, or nγ – nα)
____________ occurs when a preexisting crystal undergoes a transformation due to a change in pressure or temperature. This commonly occurs in minerals that have different crystal structures and different symmetry at different temperatures or pressures.
Twinning
Due to compositional changes during crystal growth
Zoning
Spatial variation in birefringence caused by a bent crystal lattice.
Undulatory extinction
A process by which a solid solution phase unmixes into two separate phases in the solid state.
Exsolution lamellae
An intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution (unmixing of two minerals).
Perthite
An intergrowth arising due to exsolution where potassic feldspar is present as blebs or lamellae within a sodic feldspar.
Antiperthite
When sodic and potassic feldspars are in broadly equal abundance.
Mesoperthite
Perthite that can only be observed with the aid of microscope is known as __________.
Microperthite
Minerals that shows complete solid solution at higher temperatures, but do not show such solid solution at lower temperatures.
Exsolution
Intergrowth of branching rods of quartz set in a single crystal of plagioclase, neighbouring rod of quartz have the same lattice orientation and extinguish together. May also occur at grain boundaries of K-feldspar.
Myrmekite
An igneous texture in which an intergrowth of two minerals has the appearance of runic writing.
Graphic texture
Rocks containing abundant graphic texture can be described as ________.
Granophyric
A solid solution phase unmixes into two separate phases in the solid state and it occurs only in mineral whose compositions vary between two or more pure endmember compositions.
Exsolution lamellae in pyroxene
The same dimensions in all directions (garnet, spinel)
equant
equant with a nearly square cross sections (halite, galena)
blocky
Needle like (actinolite, sillimanite)
acicular
Appearing to be a plates or a thick sheet (gypsum, graphite)
tabular, platy
Hairlike or threadlike (serpentine)
capillary or filiform
Elongated and flattened in one direction (kyanite, wollastonite)
bladed
Elongated with faces parallel to a common direction (apatite, beryl)
prismatic or columnar
Easily split into sheets (muscovite, biotite)
foliated or micaceous
Appearing as a solid mass with no distinguish feature
massive
Composed of many individual grains
granular
Containing crystals emanating from a common point
radiating or divergent
Composed of fibers
fibrous
Appearing stalactite shaped
stalactitic
Appearing like flat plates or slabs growing together
lamellar or tabular
Containing an aggregate of crystals giving starlike appearance
Stellated
Having feathery appearance
plumose
Appearing like a branching tree or plant
arborescent or dendritic
Net-like, composed of slender crystals forming a lattice pattern
reticulated or latticelike
Made of spherical/hemispherical shapes made of radiating crystals.
colloform or globular
Having an appearance similar to a bunch of grapes
Botryidal
Having a kidney shaped appearance
Reniform
Having surface covered with fine crystals
Drusy
Composed of very small or small spheres
Elliptic or pisolitic
Having a planar composition surface separating 2 individual crystals {021}.
contact twinning
Have an irregular composition surface separating 2 individual crystals {001}.
penetration twins
Compositions surface are parallel to one another, they are called _________ {010}. Plagioclase is the common example of this type of twinning.
polysynthetic twins
If the composition surface are parallel to one another, they are called ________. Occurs in chrysoberyl along a {031} plane.
Cyclical twins
