# Shared Flashcard Set

## Details

GEO 416k
Exam 2
47
Geology
11/09/2010

Term
 Anisotropic Minerals
Definition
 1) The velocity of light varies depending on direction through the mineral 2)They show double refraction (the light entering the mineral is split into two rays with different velocities) 3) Each Anisotropic mineral has either 1 (uniaxial) or 2 (biaxial) optic axes along which they act isotropic.
Term
 Optically Uniaxial Minerals
Definition
 1) Minerals that belong to the Hexagonal and Tetragonal systems 2) Have one optic axes
Term
 Optically Biaxial Minerals
Definition
 1) Minerals that belong to the orthorhombic, monoclinic, and triclinic systems. 2) Have two optic axes
Term
 Interference Colors
Definition
 1) The colors  produced because of light split into two rays passing through a mineral under crossed polars.
Term
 Ray Retardation (Δ)   Δ = d(V/Vs-V/Vf)
Definition
 1) The distance that the slow ray is behind the fast ray after both have excited the crystal. 2) The magnitude of the retardation depends on the thickness of the crystal plate (d) and the differences in the velocity of the slow ray (Vs) and the fast ray (Vf)
Term
 Anisotropic Double Refracted Light Rays
Definition
 1) Plane polarized and vibrate at right angles to each other. 2) Ray with lower index of refraction (n) is called the fast ray, and the ray with the higher index of refraction is called the slow ray (retarded).
Term
 Birefringence (δ)   δ = (ns - nf)
Definition
 1) The difference between the indices of refraction of the slow (ns) and fast (nf) rays. 2) Numerical value depends on path of light through the mineral. 3) Paths along optic axes show zero Birefringence.  4) May vary depending on wavelength of light.
Term
 Interference of Two Rays
Definition
 Two waves travel in the same plane and the same direction. 1) In Phase: two rays are vibrating at right angles, the resolved components are in opposite directions and therefore destructively interfere and cancel each other. No light passes through the polarizer and the mineral grain appears dark 2) Out of Phase: resolved components are in the same direction, light constructively interferes and light passes the upper polarizer.
Term
 Orders of Interference Colors
Definition
 Go through a repeating sequence, with change from red to blue occurring at retardations of approximately 550, 1100, and 1650 nm. 1st order: less than 550 nm 2nd order: between 550 - 1100 nm 3rd order: between 1100-1650 nm The higher order, the more washed out the color
Term
 Parallel Extinction
Definition
 The mineral is extinct when the cleavage or length is aligned with one or the other of the cross hairs. The extinction angle is zero degrees
Term
 Inclined Extinction
Definition
 The mineral is extinct when the cleavage or length is at some angle to the cross hairs.
Term
 Symmetrical Extinction
Definition
 The mineral displays either two cleavage directions or two distinct crystal faces to which two extinction angles can be measured, one from each cleavage or crystal face. If the two extinction angles are the same, the mineral displays symmetrical extinction.
Term
 No Extinction Angle
Definition
 Mineral does not display an elongate habit or prominent cleavage. They go extinct once in every 90° of stage rotation, but no cleavage or elongation is available from which to measure an extinction angle.
Term
 Undulatory Extinction
Definition
 Extinction in a grain follows an irregular or wavy pattern. Due to deformation of rocks, grains may be bent or strained and parts of a single grain are in slightly different orientations and therefore go extinct at different times.
Term
 Pleochroism
Definition
 Anisotropic minerals that display a change of color as the stage is rotated in plane light (upper polarizer removed). It is produced because the two rays of light are absorbed differently as they pass through the colored mineral and therefore have different colors.
Term
 Extraordinary Ray (ε Ray)
Definition
 Ray in Uniaxial Mineral that vibrates perpendicular to the ordinary ray (ω ray) and parallel to the c-axis. Velocity varies upon direction.  Optically positive: index of extraordinary ray (nε) is greater than index of ordinary ray (nω). In other words, if the ε ray is slow, the mineral is optically positive and therefore negative if fast.
Term
 Ordinary Ray (ω ray)
Definition
 Ray in Uniaxial Mineral that vibrates perpendicular to the c-axis. Ray has the same velocity regardless of path through mineral. Optically Negative: index of Ordinary Ray (nω) is greater than index of Extraordinary Ray (nε)
Term
 Indicatrix   [image]
Definition
 Geometric figure constructed so that the indices of refraction are plotted as radii that are parallel to the vibration direction of the light. Includes a principle, circular, and random section.
Term
 Indicatrix: Principal Section
Definition
 A section through the indicatrix that includes the optic axis, which is an ellipse whose axes are nω and nε.
Term
 Indicatrix: Circular Section
Definition
 A section through the indicatrix perpendicular to the optic axis whose radius is nω.
Term
 Indicatrix: Random Section
Definition
 Any random cut through the indicatrix produces an ellipse whose axes are nω and nε' where nε' is between nω and nε.
Term
 Tetragonal Minerals
Definition
 Typically prismatic and either elongate or stubby parallel to the c-axis. The faces are commonly combinations of prisms parallel to the c-axis , pinacoids perpendicular to c, and pyramids, although other forms are possible. (See Tetragonal: case 1-3)
Term
 Tetragonal: Case 1
Definition
 The crystal is cut perpendicular to the optic axis (circular section) so that light follows the optic axis and travels with index nω. If polarizers are crossed, the section should be uniformly dark on rotation, so no extinction angle can be measured.
Term
 Tetragonal: Case 2
Definition
 Crystal is cut parallel to the optic axis (Principle Section with ε axis parallel to the length of the crystal and the ω axis perpendicular to the length). Light travels through the crystal perpendicular to the optic axis. Must be parallel extinction b/c vibration directions for ω and ε are parallel to the width and length.
Term
 Tetragonal: Case 3
Definition
 Crystal is cut along a random angle. Birefringence is intermediate. All three cleavages are visible. nε intermediate. Extinction to the prismatic cleavage is parallel, symmetrical, or anything in between. The ω ray vibrates parallel to the trace of the pinacoidal cleavage, so extinction is always parallel to cleavage.
Term
 Hexagonal Minerals
Definition
 Common forms: prisms, pinacoids, pyramids, and rhombohedrons, although a number of other forms are possible.  Common cleavages: prismatic, pinacoidal, and rhombohedral See Hexagonal: Case 1-3
Term
 Rhombohedral Cleavage
Definition
 Three cleavage planes that intersect at angles other than 90° [image]
Term
 Prismatic and Pinacoidal Cleavage
Definition
 Crystal with three prismatic {100} cleavages that intersect at angles of 60° and 120° and a {001} pinacoidal cleavage at right angles to the c-axis.
Term
 Interaction of light with minerals
Definition
 1) Reflection: luster 2) Speed 3) Index of Refraction: n = velocity of light in vacuum/ velocity of light in mineral; measures how effective a mineral is at bending light as it passes from one material to another.
Term
 Snell's Law
Definition
 sinθ1/sinθ2 = n2/n1 = speed of light in mineral/ seed of light in air large difference between n of mineral and n of its surroundings means that it will stand out and have high relief. Small difference means it will have low relief.
Term
 Normal Dispersion
Definition
 Increase in index of refraction (n) with decrease in wavelength (λ)
Term
 Abnormal Dispersion
Definition
 Decrease in index of refraction (n) with a decrease in wavelength (λ).  Example: Halides; some light absorbed by mineral
Term
 Translation Operations
Definition
 1) Periodic repetitions along vectors 2) Translation of ions - achieved in: 1-D: Row Lattices 2-D: Plane Lattices 3-D: Space Lattices
Term
 Lattice
Definition
 An imaginary pattern of points (or nodes) that has an environment that is identical to any other node in the pattern; repetition of a patter
Term
 Space Lattices
Definition
 Produced by translations along two vectors- repeated with constant distances and angles.
Term
 Plane Lattices
Definition
 Oblique Net  Rectangular Net Centered Rectangular Net  Diamond Net Hexagonal Net Square Net
Term
 Plane Lattice: Oblique Net
Definition
 p = primitive, nodes only at corners
Term
 Plane Lattice: Rectangular Net
Definition
 P = primitive, nodes only at the corners
Term
 Plane Lattices: Centered Rectangular and Diamond Net
Definition
 c = centered, node in the middle and at the corners (diamond is primitive)
Term
 Stacking of Oblique Nets
Definition
 Stacking of an oblique net (or plane lattice) at an arbitrary angle results in primitive triclinic lattices
Term
 7 Lattice Systems In order from least to most symmetric
Definition
Term
 Triclinic Crystal System
Definition
 Described by vectors of unequal length, as in the orthorhombic system. All three vectors are not mutually orthogonal (δ,β,α ≠ 90°). Least Symmetric and is the only lattice type that has no mirror planes. Mineral examples include plagioclase, microcline, rhodonite,  turquoise, wollastonite and amblygonite, all in triclinic normal (bar 1).
Term
 Monoclinic Crystal System
Definition
 Described by vectors of unequal length (a≠b≠c) as in orthorhombic system. They form rectangular prism with a parallelogram as its base.(δ,α=90°,β≠ 90°). Two lattices exist: Primitive and Centered[image]
Term
 Orthorhombic Crystal System
Definition
 Lattices result from stretching a cubic lattice along two of its orthogonal pairs. (a≠b≠c) and (δ,α,β=90°). Lattices include: simple orthorhombic, base centered, body centered, and face centered. Common minerals include Olivine, Aragonite.
Term
 Tetragonal Crystal System
Definition
 Two Lattices: Simple Tetragonal, Centered Tetragonal. Common minerals: rutile, zircon, pyrolusite, mulfenite, chalcopyrite. (a=b≠c) and (δ,α,β=90°).
Term
 Hexagonal Crystal System
Definition
 has only one lattice type: simple hexagonal. Common Mineral: Graphite.(a=b=c) intersecting at 120°. Has 4 Miller indices.
Term
 Isometric Crystal System
Definition
 "cubic" crystal system where unit cell is a cube. The most common and simplest shapes found in crystals and minerals. Three varieties of crystals: simple cubic, body-centered cubic, and face-centered cubic. Native minerals are common (lead, aluminum copper, gold, iron, chromium)
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