OPTICAL MINERALOGY PDF
Mineralogy and Optical Mineralogy by M. Darby Dyar and Mickey E. Gunter The unique aspect about the textbook Mineralogy and Optical Mineralogy is the. minerals. The most general application of optical mineralogy is to aid in the identification of minerals, either in rock thin sections or individual mineral grains. PDF | On Jul 5, , Ibrahim M. J. Mohialdeen and others published Binrawai Xawakan (Optical Mineralogy).
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Optical Mineralogy in a Nutshell. Use of the petrographic microscope. Slides borrowed/adapted from Jane Selverstone (University of New Mexico) and John. Optical Mineralogy (3rd Ed) [Paul F. Kerr] McGraw-Hill - Ebook download as PDF File .pdf), Text File .txt) or view presentation slides online. Mineralogía Óptica. Nesse - Introduction to Optical Mineralogy - 3th resourceone.info - Ebook download as PDF File .pdf) or read book online. The third edition of Introduction to Optical.
For example, if Rlmineral is greater than Ricement the Becke line will appear to move into the mineral when the microscope tube is slowly racked upwards. If the RI of a mineral is close to that of the cement then the mineral surface will appear smooth and dispersion of the refractive index may result in slightly coloured Becke lines appearing in both media.
The greater the difference between a mineral's RI and that of the enclosing cement, the rougher the surface of the mineral appears. An arbitrary scheme used in the section of mineral descriptions is as follows: Habit This refers to the shape that a particular mineral exhibits in different rock types. A mineral may appear euhedral , with well defined crystal faces, or anhedral, where the crystal has no crystal faces present, such as when it crystallises into gaps left between crystals formed earlier.
Other descriptive terms include prismatic, when the crystal is elongate in one direction, or acicular, when the crystal is needle like, or fibrous , when the crystals resemble fibres.
Flat, thin crystals are termed tabular or platy. Cleavage Most minerals can be cleaved along certain specific crystallographic directions which are related to planes of weakness in the mineral's atomic structure.
These planes or cleavages which are straight, parallel and evenly spaced in the mineral are denoted by Miller's indices, which indicate their crystallographic orientation. Some minerals such as quartz and garnet possess no cleavages, whereas others may have one, two, three or four cleavages. When a cleavage is poorly developed it is called a parting.
Partings are usually straight and parallel but not evenly spaced. The number of cleavages seen depends upon the orientation of the mineral section. Thus, for example, a prismatic mineral with a square cross section may have two prismatic cleavages. These cleavages are seen to intersect in a mineral section cut at right angles to the prism zone, but in a section cut parallel to the prism zone the traces of the two cleavages are parallel to each other and the mineral appears to possess only one cleavage e.
Relief All rock thin sections are trapped between two thin layers of resin or cementing material to which the glass slide and the cover slip are attached.
The refractive index RI of the resin is 1. The surface relief of a mineral is essentially constant except for carbonate minerals , and depends on the difference between the RI of the mineral and the RI of the enclosing resin. The greater the difference between the RI of the mineral and the resin , the rougher the appearance of the surface of the mineral.
This is because the surfaces of the mineral in thin section are Alteration The most common cause of alteration is by water or C0 2 coming into contact with a mineral, chemically reacting with some of its elements, and producing a new, stable mineral phase s. For example, water reacts with the feldspars and produces clay minerals. In thin section this alteration appears as an area of cloudiness within the transparent feldspar grain. The alteration may be so advanced that the mineral is completely replaced by a new mineral phase.
For example, crystals of olivine may have completely altered to serpentine, but the area occupied by the serpentine still has the configuration of the original olivine crystal. The olivine is said to be pseudomorphed by serpentine. Isotropism Minerals belonging to the cubic system are isotropic and remain dark under crossed polars whatever their optical orientation.
All other minerals are anisotropic and usually appear coloured and go into extinction that is, go dark four times during a complete rotation of the mineral section. This property, however, varies with crystallographic orientation, and each mineral possesses at least one orientation which will make the crystal appear to be isotropic. For example, in tetragonal, trigonal and hexagonal minerals, sections cut perpendicular to the c axis are always isotropic.
Commercially available as a CD. Experiments in Crystal Optics -- Hans Dieter Zimmermann; The purpose of the experiments below is to impart an intuitive understanding of the interaction between light and crystals and thus, of optical crystallography. This will help to demystify what is seen in the polarizing microscope and will better prepare students for the introduction of optical indicatrices as 3-D models to describe the directional dependence of light velocities, and thus refractive indices in anisotropic crystals.
Laboratory Exercises and Demonstrations with the Spindle Stage -- Mickey Gunter, University of Idaho; The goal of this lab session is to introduce you to the spindle stage and its possible uses in an undergraduate mineralogy lab. At the undergraduate level, it can be used to identify minerals and to demonstrate the relationships among grain shape, retardation, and interference figures.
Therefore, this exercise is primarily intended to be used in an introductory physical geology class, perhaps for advanced students or as an extra credit project.
It may also be appropriate as a brief introduction "teaser"? North Dakota; Many compounds crystallize rapidly from evaporating solutions, and many can be crystallized from melts. Because of this, it is possible to do simple crystallization experiments and to watch crystals grow over short time periods.
Students can study several different compounds during one lab period. Students can examine many things quickly and easily, including crystal habit, growth zones, nucleation, deformation textures. North Dakota; This exercise continues the study of the physical properties of minerals and introduces petrographic microscopes. North Dakota; Students look at mafic igneous minerals, learning to distinguish and identify them in hand specimen.
If Lh e fi eld stop in the eyepiece to a rotating nose piece.. Thc IIuygenian ocular is frequently called a negative ocular. Parts of the Microscope. TIlese are usually used in combination with 40 mm or 16 mm or cOlTesponding objectives.
The foca l plane li es below the field lens and the object image is form cd by th l ohjcctive in lhi:. The ocular consists of a tube which fits snugly into the tube of the microscope. An eye lens is located above and a field lens below. A diagram showing the path of light through the microscope. Huygenian ocular.
Oculars used in modem petrographic microscopes are ordinarily of the Huygenian type or a simple modification. The names of the mechanical features are largely self-explanatory. An optical pattern is obscrved in the eye. Where 'ombinations giving higher magnifications are desired. Such corrcction is particularly impor. Sections of positive reclcd cyc-Icns arrangement giving a flat and negative oculars. American Optical Co. The eyepiece as a whole has no external focal plane on the field-lens side.
The pupil of the eye is placed at this level to observe the interfercnce figure. III ol'dor lo securo Ih n h 'st I' 's lilts. Diagram showing the relative dimensions of the different fields in the microscope and their relation to the illumination. A realistic flat picture of the object is formed in the eye. After Belling. The image plane and the plane of the crosshairs should coincide.
Huygenian ocular a negative ocular Objecttve Sample Condenser t: Field diaphragm Mirror FIG. A visual ReId stop with crosshairs. The parts of a polarizing microscope equipped either with polarizing plates or nicols are indicated in Figures The lized when the dimensions of particudrum records the movement of a crossline which traverses the field of view.
These are also calibrated for different lens combinations with a stage micrometer. Fi gure h as observed a t the eye are govern ed by relations b etween th e objec li ve. In this objective practically all the images produced by the different colors of I li e sp ectrum lie in the same plane and are equally sharp. Such eyepieces are useful in determining the axial angle of interference figures with the microscope.
Th e dimensions represented by the divisions in the micrometer ocuhu. Micrometer eyepieces are also utiFIG. In the case of achromatic objectives correction of aberrations of the image becomes more difficult with high eyepiece magnification. Views of several cut objectives appear in Figure The movement is recorded on a drum at the side of the eyepiece. Apochromatic objectives are constructed to prOVide additional color 'o rrection b eyond that usually given by achromatic objectives.
The eye lens is focused on the scale. A fine line through the center of the field parallel to the screw axis serves as a guide in orienting the object with reference to the direction of movement of the crossline. Carl Zeiss.
The Filar micrometer eyepiece Figure is designed for accurate horizontal measurement across the field of view. A small cross line is moved to and fro. The problems of securing good fluorite and the practical difficulties in their manufacture are consiti nahle. Manufacturers usually supply as standard equipment The filar micrometer.
Achromatic objectives are ordinarily used for thin-section or fragment studies. The lenses are II lade of combin ations of fluorite and glass.
The Huygenian eyepiece contains a scale divided into 0. Th ose objectives are only occasionally used for II li 'l'os 'op ic sl ild y or min erals. Ordinary 5 X and lO X oculars are satisfactory for most work with the polarizing microscope.
In the lower section of the field. Sectional views of objectives. III ' magnification may b e said to be "useful.. After L eitz. I"or praclical p urp oscs the uppcr limit of "useful" magnification with 0 polari zin g microscopc is about Oil-immersion objectives are used for high magnifications where a high degree of resolving power and correction are required. This figure multiplied by the power of the eyepiece gives the magnification for a standard tube length.. Diagram illustra ting the conve rgence of ligh t by means of cedar oil placed in front of the lens of an oil-immersion objective.
After use the oil should b e removed by the use of lens p ap er moistened with xylol or b enzine. In two objectives haVing the same focal distance and therefore the same magnification.
The effect of oil immersion on the cone of light entering the front lens of an oil-immersion objective is shown in Figure A good oil-immersion objective. The objective should be handled carefully. This should be corrected.. Ac hromatic. It is worthwhile.
Zeiss mm.. The numerical ap erture N.. Other things b eing equal.. T hcre are limits to the resolving power of the microscope. The microscope is primarily an instrument for magnification. The follo wing table outlines the magnifications at the eye for diffe rent combinations of objectives with an equivalent focus of Corrections may b e determined by using stage and eyepiece micrometers.
OH As long as the increase in magnification I 's lil ls in b etter vision of an object and more definite separation of detail. Several manufacturers stamp the initial magnification for a standard mechanical tube length 3 on the objective. The working distance is the distance b etween the objective and the top of the cover glass of the microscope slide when the objective is in focus. The working distance of an oil-immersion objective is very short. A po ' hrom a t ic oil imm ersion EquivaMagnificatio ns lent Mag ni fiwit h ocul a rs cation focus..
The numerical aperture furnish es a criterion of the quality of an objective. The oil should agree in both dispersive power and index of refraction with the front lens of the objective.
A po ' hromat. It serves to 1". I Ih' Iy pe sel cclcd forillu slrali on. It not only serves as a comparison object for determining the magnification of the microscope but also may be used to give the magnification of micro drawings. More elaborate microscop es t Fi gllJ"c are fined with a mea ns [or rota tin g. Either may b e inserted or withdrawn from the optical path at will. It may be set at any angle through but is usually kept adjusted to a plane at right angles to the plane of the analyzer.
Lines per inch separated 1. The device was originally used by Amici and was later oI d: Amici-Bertrand L ens. Am erican Optical Co. Several may be given as follows for blue light wavelength The nicol prism or polarizing plate mounted in the tube of the microscope above the objective is known as the analyzer. It has been shown mathematically that the limit of resolution equals the wavelength divided by twice the numerical aperture.
From the standpoint of increase in resolution or detail. For superior results.
This might be d escribed as the distance apart of two object points in the field of view of the microscope whose disk images would just touch as projected to the eye. IlIlerference figures may b e observed without the Amici-Bertrand lens il lli c ocular is removed.
The stage micrometer is a glass slide carefully ruled into hundredths of a millimeter or 0. A sectional view showing a prism in position in the substage assembly. The nicol is carried on a sliding mount Figure while in some models the plate Figure flips downward into the optical path. From this relationship it is possible to compute the number of lines per inch that can be separated by different numerical apertures. Enlarged photomicrographs of this type. A common form of projection is the enlargement employed in taking photomicrographs.
Thus magnification ratios of T llfCO co mpon ents may be present in a condenser system. Such increase in magnification above the magnification of the microscope is essentially enlargement and does not result in increase in resolution.
The limit of resolution for green light with a lens of N.. Photomicrographs taken with a camera having a long bellows may increase the magnification ratio given by the microscope several times. III work in g willi hi gh powC'r or in obtainin g inter-.
This lens is inserted in the tube of the microscope between the ocular and the analyzer Figure A polarizing plate mounted in the substage assembly is shown in Figure The plane of vibration is normal to the plane of the polarizer and is usually either p erpendicular or horizontal in the fi eld of view. The cross hairs in the eyepiece are set parallel to the two planes. Microscope Accessories. Immersion IOlld 'nsers are mad e to work to "..
This suffices for all objectives of N. It is employed in the d etermination of the order of interference colors bel: In the case of higher numerical apertures a special lens is inserted in place of the condenser in the movable mounting. Optical Co. The plate forms a window in the compensator and is rotated by turning a graduated drum. The compensator is designed to fit the tube slit above the objective in the same opening used for the gypsum and the mica plates.
The qu artz w edge is ground to produ ce interference colors from the beginnin g of the first to th e end of the third or fourth ord er. Berek Compensator. Iris Diaphragm. A calcite plate with the c-axis vertical is inserted in the accessory slot of the microscope. These are marked with arrows indicating the fast.
A mica plate with. The accessories provided with the microscope generally include a quartz wedge. Thus slides FIG. It is advanta American Optical Co. The arrangement of the condenser. A diagram illustrating the conduces a convergent beam. The iris diaphragm is attached to the lower side of the tube that holds the polarizer. Lo ng slides. It is especially useful in high-power examination. OlJiect Slide. The slow-ray directions in both the mica and gypsum plates are indicated.
Glimmer and Gips. I 'a ' 1' importance. It serves to reduce the cone of light. Th e concave mirror converges the light upon the object. This is more effective if used with oil immersion. The adjustment is used both for measuring depth and for focusing on objects at high magnifications. The rolation of the compensator nee 'S5ary to bring this about is a Ill 'asure of the retardation. Sli ch sli des fit easily on the rotating. Th e relationship b etween a coarse and fine adjustment and the detail of the fine adjustment for one type of microscope are illustrated in Figure The fine ad justment.
Various lengths d lid widths of object slides may hI' Iised. It is marked and mOl1n ted as shown in F igure 2. Fine Adjustment.
Ilili ': The student should assume an erect but not too rigid position. The Berek Compensator. It is assumed that the top of the slice is pressed t c. Fine-textured lens paper or. Even under the h es t conditiolls mi crosc lpe work prodll ' 's: If it is difficult to do this at IIrst.
II willdow in the accessory plate. High-power or oil-immer1'" '. Properly Ilscd. Leitz Inc. The quartz wedge mounted on a glass plate and in a metal frame. This applies to the ocular. A few. Most of the precautions to be observed in the use of the instrument are such as should be applied to any piece of fine apparatus.
Objectives should be brought into focus by moving the tube of the microscope upward rather than downward. Objectives usually employed for thin-section work are corrected by the manufacturers for a cover-glass thickness of from 0. In order to obtain the best results with objectives.
The arrow marks the slow-ray direction. The gypsum plate a. Both eyes should b e kept open while looking through the instrument. It is also a good plan to learn to observe equally well with either eye and not to de. Care of the Instrument. Possibility of contact between the lower lens of the objective and the thin section is thus I". Mica avoided.. A cOlllpensator to mcaSUl e llilo ill dili'ercnces in retardation. A polarizing microscope is expensive. Precautions to Be Observed in the Use of the Microscope.
In case the slide is poorly mounted and a space intervenes b etween the top of the slice and the bottom of the cover glass. It is essential. Ordinarily a wedge covers four orders from the thin edge to the thickest portion Such a position with the microscope tube inclined allows him to work with maximum comfort.
The use of annular diaphragms develops a change in optical path. The theory and application of phase microscopy have been reviewed at some length by Bennett et al.. Phase Microscopy. Oll t ra st may he produced by conb'ol Iii IIJiv! Various types of artiRcial illufound considerable application in mination for the microscope: B ausch and Lomb Optical II '. Phase differences between light waves passing through points in the mineral and in the surround are utilized to bring out contrast at the eye.
Minerals with extremely low relief in balsam may be made to stand out more distinctly with this arrangement. Where the. In the examination of minerals the technique of late has received some attention. These consist of various types of electric bulbs mounted in cases with a speCial blue-glass light filter in the path of the illumination. At ordinary magnifications a good north light with a broad.
Bausch and Lomb Oplacking in contrast may be illumitical Co. A strong lamp for general utility. The beam from the arc is very warm and should always be passed through a cooling cell of water in order to avoid injuring the cement in the prisms of the microscope unless special prisms are employed. The technique of phase microscopy has FIG.
Tlu'ee types are illustrated in Figure a. At high magnifications and for photomicrographic work a mechanical-feed arc lamp is sometimes used. Patterns of annular shape which introduce a phase shift of one-quarter wavelength of green light have been found effective. A phase-shifting element may be mounted at the rear focal plane of the objective. A low-vollage lamp with V-slots for filters. An annular aperture diaphragm is placed at the front focal plane of the substage condenser.
In case the refractive index of a mineral less than about 10". In case such illumination is not available.
A low-voltage bulb with a condensing lens and diaphragm.. The two annuli when. An annulus at the level of the condenser diaphragm and a diffraction plate at the back focal plane of the objective are utilized to produce phase differences Figure When illuminated it furnishes a light.
In the latter case a special study of equipment available on the market is desirable. The exposure may b e determined with the photometer. Lawrence Co. Phase contrast. Where retardation of undiffracted light occurs. These may be obtained quickly with simple equipment unless prints of exceptional quality are reqUired. Courtesy Dr.. An exposure meter is placed be" Annular tween the viewing lens and the camera.
Carl Z eiss. The range in diameter of the kaolinite particles a and Eyepiece b is 2 to 6. Good quality microscope lamps with Am erican Optical Co.. A small camera designed for mm film may be fastened to a tube above the microscope Figure The excellence of the photoFIG. Photographs of thin sections are frequently desired for purposes of record.
For example. Both "bright" an d "dark" contrast are illustrated.. The exposure reading for each exposure. A viewing lens is attached to the side of the C"d"". Focus may be adjusted with the aid of the viewing lens.
Mounts c and d were immersed in a mixture of butyl carbitol and clove oil n When a satisfactory exposure has been secured. West Germany. Microphotographs of clay minerals by pllase contrast technique.
Phase contrast arrangemicrographs secured will depend upon ment with an annular diaphragm the quality of the illumination. In Figure photographs taken at magnifications of Study of photomicrographs in various textbooks and professional journals will serve as a gllide in selectin g areas slIitahle for phoLography.
The range in diameter of the halloysite particles c and d is 2 to '-Focal point of Where larger photomicrographs are desired cameras equipped for cut fi lms or plates may be uscd in place of the small camera mentioned above. If it does not. Centering the Stage with the Field. A small pin usually fits into a notch at this position.
A slide ' lIlaining a small natrolite crystal IIlay be placed upon the stage be. Ordinarily these are set by the optical firm supplying the microscope. Screws on the side of either the objective collar or the stage Figure are used to align the tube axis and the stage. The lower nicol is adjusted at right angles by rotating it in the substage collar until the field becomes dark. Crossing the Nicols. The nicols should remain in th e position giving maximllm darkn css.
This is true in each of the four positions 01 'x till ction.
The point should describe a concentric circle of rotation about the intersection of the cross hairs. A simple procedure is fol. Diagram illustrating centering the field of view of the microscope. G The nab'olite becomcs dark between crossed nicols when I he edges of the crystals are parallel 10 the vibration directions.
The plane of vibration of the analyzer is usually fixed by the manufacturer either from left to right or up and down as one observes the microscopic field. Testing the adjustm ents of I w 'on crossed nicols and turned until the crosshairs with natrolite fragments. The planes Courtes y of Paul Rosenthal. Aftcr the other oI lijl lslllll'lIl s l"l ve 1 ' '11 Iliad e.
If the crosshairs dl'0 in adju stment. Four separate steps may be outlined to arrange the polarizing microscope for the examination of thin sections: Photomicrographic camera. A slide containing small elongated rcctangular crystals of natrolite FigII1'C is useful to test the setting of the crosshairs with the planes of I hc nicols. Rotate the stage. In either case it is important that the hair lines be parallel to the planes of vibration of the two nicols. The adjustment should be checked occasionally.
While looking through the instrument at the field of view. The stage is centered when the axis of rotation coincides with the tube axis of the microscope. II becomes dark. Tourmaline Figure a has maximum absorption when it is oriented with the c-axis usually the long direction of a crystal or fragment in a direction at right angles to the plane of vibration of the polarizing prism.
McGraw-Hill Book Company. Verlag Gebriider Bomtraeger. Ernest E.
Alva H. Biotite Figure b. H eidelberger 13eitr.. Helen Jupnik. Phase Contrast. Harold Osterberg. These indicate either the vibration direction or the normal to the vibration direction. Van Nostrand Company. Die Phasenkontrastmikroskopie als Hilfsmittel zur Bestimmung feinkorniger.
Determining the vibration plane of the lower nicol: Note the positions of greatest' and least darkness. I D3fl. As a result of these developments the explanation of light seems to rest upon two apparently contradictory theories. Our present effort is to understand how this is.
Optical Mineralogy And Its Uses
The distance b etween two successive crests or troughs. The medium is the ether. Several prominent theories have been advanced. The fo rm of displacement represents a curve combining movement around a 'i rcle with motion along a straight line. The source of the light and its effect on the eye are apparent. Since light crosses interstellar space.
Later experiment demonstrated that the quanta of Einstein were of the same size as those postulated by Planck. D isplacement. The theory of Huygens. As a result of the work of Maxwell. Einstein has stated as follows: We have good proof that both waves and particles exist.
Toward the end of the last century evidence began to appear that did not accord with the electromagnetic theory. TTcrlz succeeded in produ Cin g waves having propcrties: W avelength. At about this time Planck developed the assumption that radiating oscillators in a black body radiate energy discontinuously in units called quanta.
In anisotropic crystals it is not perpendicular except ill limited directi0ns. According to Maxwell. Modern studies h ave shown. Then the electron was discovered in The phenomena of light such as reflection.
It was found that the space around certain metals would become electrically conductive when the metal was exposed to light. The composition of a two-point view has not yet been found. It is a quest of science in which our present methods are imperfect. The nomenclature of the wave thcory used in this text is summarized in the follOwing paragraphs. Einstein in suggested that the absorption of light in the photoelectric process might also be in quantum units.
The vibra tion direction lies in the wavefront and is perpendicular to the ray II I iso tropic m edia. Nomenclature of the Wave Theory. Another theory was Rrst advanced by the D utch scientist Christian Huygens in the latter part of the seventeenth century.
Optical Mineralogy and Petrography
This was based on the fact that expulsion means energy. According to one. According to Huygens. This is generally referred to as the corpuscular theory. This led to the assumption that the light was concentrated in points and not uniformly distributed. Speaking of the two theories.
The corpuscles travel through space in straight lines and eventually reach the eye. Other phase differences may occur. The phasal difference represents th e portion of a wavelength by which one wave train fails to match the other. These are connected with two other vectors distinguished in isotropiC media by their magnitude and in anisotropic media also through variation in direction.
The number of vibrations in a given unit of time.
In anisotropic media the vector is still parallel to the plane of the wavefront but. The straight-line path followed by light in moving from one point to another in a given medium. In anisotropic bodies it has been shown to correspond to either the electrical displacement electric vector or the electrical field. The relative position of corresponding points on different waves moving along the same line.N ela Specialty Division.
Any section through the indicatrix which includes the optic axis is called a principal section, and produces an ellipse with axes n omega and n epsilon. By taking a series of slices through the indicatrix, at right angles to the wave normals, it can determined that the vibration directions for all paths of light emerging from the indicatrix.
This property, however, varies with crystallographic orientation, and each mineral possesses at least one orientation which will make the crystal appear to be isotropic. Thc IIuygenian ocular is frequently called a negative ocular. High-power or oil-immer1'" '.
The magnifying power, M. A mineral cut in a random orientation, with normally incident light; - The ordinary ray produced has an index, nomega and vibrates perpendicular to the optic axis.
Ihe polarizin g devic.
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