Exam 2 Flashcards
Crystal Systems
Isotropic (Cubic)
Uniaxial Anisotropic (Tetragonal, Hexagonal, Rhombohedral)
Biaxial Anisotropic (Orthorhombic, Monoclinic, Triclinic)
Uniaxial Anisotropic
Contains two indices with an optic sign that is either positive or negative; Tetragonal, Hexagonal, Rhombohedral
Crystal Morphology
When crystals are grown they develop “face” characteristics which are related to the structure. These face structures will always remains CONSTANT
Equant
Equally developed crystal form
Columnar/ acicular
long developed crystal form
Tabular
flat developed crystal form
Biaxial Anisotropic
Has 3 indices with an optic sign that is either positive or negative
(Orthorhombic, Monoclinic, Triclinic)
Pleochroism
material demonstrates a change in hue or intensity of the hue when its orientation changes under the polarized light (when you spin it on the stage)
Retardation
Birefringence x thickness x 1000; when light moved through crystals at different rates due to their RIs, which causes one be slowed down at a different rate than the other.
Birefringence
The optical property of a material having a refractive index that depends on the polarization and propagation direction of light; basically they demonstrate intereference/polarization colors (the equation is retardation / (1000 x thickness) (rhomb)
Isotropism
Light vibrates the same way when light is vibrated in a different direction (does not show up under polarized light)
Anisotropism
different properties show when moving an object and when light is placed (you’ll see it under polarized light)
Orthoscopic
usual manner of viewing things through a microscope
Conoscopic
When viewing with a cone of light; specialized way of looking like through a removed eye piece into the back focal or through the betrand lense.
Double Refraction
Erasmus Bartholinus when he reported that when he looked through a Calcite Rhomb, the singular dot he put on the paper turned into two.
Calcite Rhomb (Icelandic Spar)
When looking at a dot through it, two appear. One moves around and the other looks as though it is on a different plane. When using a polaroid, one disappears, and when two are moved together the film turns entirely dark when positioned a certain way,
Starch Grains ID
The presence of the Roman Cross.
Parallel Extinction
goes extinct in the N-S and E-W direction
Oblique Extinction
Any other angle
Symmetrical Extinction
45 degrees
Uniaxial Indicatrix figure (what shape it is and the sections it has)
Indicatrix for a uniaxial substance is an ellipsoid of revolution; it is “elongated” or “prolate” when the optic sign is positive and “flatten” or “oblate” when it is negative.
Contains the principal section (contains optic axis), circular section is perpendicular to the principal axis and a random section which cuts through when the principal and circular intersect.
Isotropic Indicatrix:
The indicatrix is a three‐dimensional plot of RI versus vibrational direction.
Biaxial Indicatrix Figure
Triaxial Ellipsoids; with 3 axes, x, y, zero (gamma, beta, alpha)
Uniaxial interference figure (how does it look?)
cross with yellow and blue quadrants, cross doesn’t disappear when moved. yellow is subtractive while blue is additive
Biaxial Interference figures (their formulas that make their colors show)
parabolas that move when the stage moves.
(gamma - beta) > (beta - alpha) ; blue on outside, yellow inside, then optic sign is positive
(gamma - beta) < (beta - alpha); yellow on outside, blue on inside, then optic sign is negative
“ω” or “o” ray (omega); “E” or “e” ray (epsilon)
the two principal refractive indices that exist in uniaxial indicatrix.
“a”-alpha, “B”-beta, and “γ “-gamma rays
three semi unequal axises of the ellipsoid
Optic Sign (eq. for uniaxial)
e - w = optic sign
(blue in 1 and 3 is positive ( E > w) while yellow in 1 and 3 is negative) (E < w)
Trace of the Optic Axial Plane (OAP)
The plane containing the optic axises along with gamma and alpha.
Optic Normal (OP)
optic normal is vertical and the optic plane is horizontal and is seen when viewing down Y, which is the normal of the two axises (perpendicular to the optic plane)
Sign of Elongation
Shows which vibrational direction allows polarized light to travel the fastest through it.When the crystal length is also the high index direction, SoE is positive if the length is low index, low index = negative SoE
Optic Angle
(2V, 2H, 2E); axial angles
2V (true optical axis of the crystal)
2H (optical axis angle in the oil)
2E (optical axis angle in the air)
(2E is always larger than 2V.)
Tobi’s Method
(d/D); relationship between angular aperture (2E, 2H, 2V) and the linear diameters of the back focal plane of the objective.
Spindle Stage or Goniometer
Rotation Device with a needle/thin object on the stage that holds a crystal in place.
EXCALIBR
Uploads the points of extinction seen from a rotating crystal on the stage which later can be used for reference when identifying other materials.
Monochromatic Interference Filter
Filters based on exploiting optical interference effects.
- Has a mirrored surface that makes destructive interference, eliminating everything except the wavelength of interest
Phase Contrast Microscopy (PCM)
A contrast technique in which light waves that pass through the specimen are changed to have different intensity. Allows easier viewing at transperent specimen like sperm cells and glass chips. Has a glow halo around what youre viewing.
(“Hoffman”) Modulation Contrast
consists of a Modulator, Objective, condenser, and a Slit (Slit allows light to come in at oblique angle so one side of image is bright and the other is dark) Allows to make a 3D looking image of the specimen.
Bright Field Microscopy
produces an image made from light that is transmitted through a specimen against a light background
Dark Field Microscopy
shows the specimen against a dark background and provides good resolution
Dispersion Staining (D.S.)
Differences between RIs dispersions of a particle and the liquid medium in which it is immersed in. The contrast technique that utilizes a central stop and an annual stop to produce colored particle boundaries, which can be used to help identify the sample
Central-Stop D.S. & Annular Stop D.S.
Annular demonstrates colors consisting of a wavelength that is that of the wavelengh matched with the RI of both the particle and the medium. (where the two RIs match, that wavelength is what will be colored); central stop is just the color complementary to the annular stop.
Differential Interference Contrast (DIC)
Used when a specimin has little to no constrast when viewed under brightfield microscopy.
Can be used to generate an image that looks almost 3D using Polarized light.
Not good to use with bifringent figures bc it causes a distorted figure.
Wayne Williams Case
tried for the murder of two individuals in Atlanta, Georgia. An essential part of the government’s case was the numerous fibers linking Williams to the murders yellow-green fibers discovered on a number of the murder. Victims were linked to a carpet in the Williams home which helped proved his guilt
Vegetable Fibers
(Seed Hairs: Cotton, Kapok)
unicellular and used as individual fibers rather than bundles. Also includes Basal fibers i think
All do complete parallel extinction except cotton
Animal Fibers
Wool, Silk, Domestic Dog/Cat, Fur Animals; all complete extinction except for silk
Mineral Fibers
Asbestos
Bast Fibers
Jute, Ramie, Sisal, Hemp, all complete extinction except sistal is a little bit iffy.
Marijuana ID by Leaf Fibers
Cystolith Hairs, Conical Trichomes, Glandular Hairs
Cotton Characteristics
Incomplete Extinction
Spiral Structure
Lumen
Undulation
Amber Retardation Color
S” or “Z” twist of Natural Fibers
S towards the right, Z towards the left
Modified Herzog Test
distinguish between bast fibers and other plant fibers. Determine the fibular orientation of bast fibers then white light from the polarizer enters the birefringent sample.
S twist = blue = positive
Z twist = yellow = negative
Synthetic Fibers
Nylons
polyesters
polyolefins (polyethylenes and polypropylene) acrylics
Saran
vinyon
elastic
glass
metallic
Regenerated Fibers
(Rayon, Acetates) Monomers (Glucose)
Polymers “Poly-glucose”
(Cellulose, Rayon)
Delustering Agents
reduces the sheen of synthetic fibers
Complete Extinction
Synthetic fibers have complete extinction
Low Birefringence:
(Acrylics, Acetates)
Moderate Birefringence
(Olefins, Nylon)
High Birefringence
(Polyester)
Cross-Striations
(Bast Fibers-Dislocated Fibrils) stripe pattern you can see, founds on bast fibers
Weaves
made out of warp and weft/fill
Knits
human and machine made
Felts
non-woven fabrics
Warp
Stronger, placed in loom first. They need to be able to take the abrasion of inserting the weft yarns across them
Weft
Runs horizontally through fabric and fills in the fabric gaps.
Plain Weave
Weft is carried over odd number warps and under the even number warps
Twill Weave
Diagonal pattern on the fabric surface
Satin Weave
wefts skip over warps and repeats on a different set of warps
Cordage Terminology
Fibers -> Yarn -> Strands -> Plies
Silk
Bombyx Mori (Looks Synthetic)
Fiber Shapes
X-Section vs Longitudinal; Cylindrical, Trilobal, Dogbone or Dumbbell, Multi Serrated
Most fibers are optically_____ except for ______ and _______
positive, acrylics and triacetates
