Mineralogy Notes PDF

## Mineralogy **M-2** Bros. ki किताब. **UNIT-1** Classmate Tue. Date 20/8/19 Page Shameem Sir ### Mineralogy 1. Indicatrix is a hypothetical concept having practical implications. 2. Quartz - 1 order grey, yellow, blue (3 types of interference colour) 3. Biotite- Light Brown, dark brown (two...

## Mineralogy **M-2** Bros. ki किताब. **UNIT-1** Classmate Tue. Date 20/8/19 Page Shameem Sir ### Mineralogy 1. Indicatrix is a hypothetical concept having practical implications. 2. Quartz - 1 order grey, yellow, blue (3 types of interference colour) 3. Biotite- Light Brown, dark brown (two types of interference colour) **All the properties of minerals are controlled by its structure.** - $9_1 = 9_2 = 9_3$: $9_1 = 9_2 \neq 9_3$ should be vertical - $d = \beta = \gamma = 90°$; $α = β = γ = 90°$ 4. Calcite has four faus of 3 hardness and two faces of 2 hardness. 5. Kyanite has two hardness 5, 7.5 6. Indicatrix is related with R.I. 7. The optical properties of the minerals are controlled by their R.I which itself are dependent upon the structure of the mineral along the crystallographic crystals. If R.I is represented in terms of certain measurements the variations in the optical properties of the minerals can be easily explained. The concept which explain these properties is called Indicatrix. (i) When we cut along $a_1$, $a_1$ becomes $⊥$ to the stage, * $I$ variation will be in the crystallo. avis by not the of the after cute tetragonal system comes after.. $a=b+C; α=β=V=90°$, (i) The mineral is considered to be a spherical object. (ii) Indicatrix is used to pass through the center of that spherical object. (iii) R.I is measured in curtain values. ⑧ Structure controls the R.I & R.I depends on the velocity of light (constant). When all the 3 sections are combined together in 3-D, we get a sphere. a_z. Sphere of Rotation, 1. There will be no change in the optical properties of the mineral irrespective of the ani's or section cut. ppl or x-nicol 2. In case of indicatrix, section is always be a circe. and hence all the radii will be equal. 3. Indicatrix will be propequal to the R.T. Smaller radii & smaller R.I * when light passes $||$ to c-axis, we cannot see the vard action along C-axis, ay * In Cubic, in polarizer in, no change in prep structure of as the velocity of light is const.. * In analyser in "Cond" cubic's are isotropic ⑥ Every circular section obtained from the indicatrix E will be isotropic ① R.Idenoted by w.. Tetragonal; $a=b+C; α=β=V=90°$. In tetragonal system the variation comes in the 'z dir. of c-axis. c-axis will always be longer than the other two. In 3D if we combine these two section (circle + ad elipse) we will get ellipsoid of 3-D. * we can have as many section (ellipsoid bad only one circular section. →→Basal Pinacord. Perism 1. If we cut vertically-> and we can have as many Such sections. 2. If we cut horizontally. 3. If we uit obliqually **In tetragonal if & I stage isotropism. or circular section paralle to the stage"** (31/8/19) Set ← Uniaxial Minerals. **The sections containing max. value of R.I are called principle sections.** 1. Principle Section → R.I-7. E&W 2. Circular Section → R.I→. W 3. Random Section R.I- &', &² 23-0 ← ciraular section If - E>w +ve - E < w > -ve Minerals / in which there is no doubt refraction is called optic axis. Minerals with one optic axis are called Uniaxial Minerals Uniavial - tetragonal - Hexagonal. -> Biaxial Minerale. (diß,r). (2 circular section). 1. I to the two optic axis - we have two circular sections. 2. Two circular sections meane two isotopic sections. In biaxial minerals- - α→ Minimum (may have any value) - β→ Medium - Constant) (not change) - Y- Maximum (may have any value. Three- Principle Section 7. Triavial Ellipsoid, - xz (L.) → yellow - XY (Σιβα) → dark green - yz (Bir), → green / dark green. Neutral Mineral B is in between 2 & Y then it has no sign and called Semi-random Section → any section in betawem the principle sections. - Semi-random- Zx'». (ẞ won't change). XZ'→ - Yz'→ - Yx' Totally random section. Χż (α'γ'). (i). Section $⊥$ to the Y (B) will be the circular section. whose radius will be equal to the B. and y direction will serve as the optic axis. Here two circular section.. Biaxial +ve $ is closer toa than to Y. & ay is the BXA. Biaxial -ve- Vibration directions are also called as bisectrix (Bx). - Bxa acute bisectrix - Bxo obtuse bisectarix C-S cirewar section. B-tve. If Bxa = Z BX = X B--ve. If Bxa=x BX0=Z (dark) (visible) Conoscopy & Orthoscopy. Tw The difference between them is in the arrangement of light Orthoscopy we will use a plane mirror. orthoscopy conoscopy orthoscopy. the light is $||$ tand extinction is always measured in the orthoscopic mode. - extinction Lis always acute angle First time birefringence was observed in Calcite. Locus of E-ray changes. Augite's extinction L is - 42°-48° while others are less than 485°. It is the differential absorption of light during the rotation of stage as light gets incident at different angles and hence we get pleachroism. Birefringenu A light is vibrating in two mutually Idirection. One is extra-ordinary ray (Exy one is ordinary ray (O-ray) E-ray has & & O-vay has is R.I. M=Sini = Constant (1). (Snell's law dis not followed by E-ray). →RP (Eray) DOOOOO R.P (0)-ray) Propagation direction are different but wibration direction are mutually 1. (Cof E-x O-rays) Path Difference →. We take a slab of thickness 't and light is incident $⊥$ to the basal pard, The ray splits into E-ray (slow) & O-ray(fast) and travels within the crystal. O-ray will pass lineard y& e-vay traverses a different path. Sinu E-vay is slow and hence by the time E-vay emerges on the other side of the slab. O-ray has already travelised a much greater distance in the same time (t' ) Interference Figure These dark or bright regions are isochromes or cones of retardation, provided we we monochromatic light. O.A/Melatope > Isogyres. Isochromes If we use Sunlight / whitalight, then bands of Concentric or circular bands of different colours and the set of colours will repeat themselves. (separated by a ring of red color). As, we move away from melatope towards margins we will get high order coloris & low order colours is towards the mulatope. Melatope- intersection of two isogyres. Melatope position of optic axis. 0.85 Highest power magnification. De O'A at the center of cross-wires, OAC Figure-> - Basal Section I c axis - Prismatic O.A. $||$ to the stage / caxis-11. - Pyramidal Section ¿-axis indived, **Random Section** If we increase the magnification we will get large and barger no. of isochromes. **Principle Section (O.A $||$ to the stage)** (but makes an $\angle$ with the cross wirer) (or vibration directious of the microscope) Diffused grey figure - we will get when O. A is $||$ to any of the Grass-wire (Stage के $||$ तो है ही). This method is useful in distinguishing different crystal sections. ie isotropic, uniaxial and biaxial sections. Uniaxial or Biaxial ? The components of Ray & Ray② on resolution overlap each other and hence, we Can say that these rays are moving perfectly $||$ to each other. These ray will Struck the analyser and there will be a path difference and whenever there will be a path difference interference will occur. (The corner rap will travel max. distance.maybe correct) Ray①. A = tx Birefringenu = tx w-e' (for uniaxial is same), Ray② Retardation will be less since thickness has reduad and as we move towards O.A, Bire- fringena decreasers and along O'A no bir efringence, Isochromes are so called becz we get soo single Colour for same Retardation, Or chromes of equal Retardation En 3-D. → as we move tawands O. A retardation decчмань as birefirengence decreases as well as thickness also decчмань, → Red lighe is the starting point.. → different / one order of interference codan, - alternate circular bands / romatic - tones of bright & dark colour Light Isochromes / cone of equal rutardation (These are the base of the cone). Cones ave the composite cones) Inclined rays will resolve within the crystal. loum) As the s(retardation) increases; Cone of equal relatoudiation incream All the inphase waves of the order of black colour are extinct as the vibration dir. will be $||$ to the polarizer. More the divergence, more the travel distama. the variation, more the thickness (divergenc from the prinuple axis of the mirror - principle axis (W) - Divergence Thickness varies and Bierefringence also varies & hence retardation varies. Prinuple axis will have R. I (W). One ray will be fast and another will be slow. -> fast of R2 will coincide with Slove of Ri. → Slow will be on the left side and fast will be on right side after resolution. -> we will geta locus of cirde and infinite no. of points. → Sinu, this an iverted cone, hence it is called cone of equal retarda- tion. The Birefringence and thickness decreases as we move from the boundary of the circle to the centre. Gied and 4, becomes zero at the O.A. At the 0.A. the light is incident normally. With the helb of this we can determine the sign of the mineral. To know the vibdir. of a microscope, we will orient the bisti to $||$ to the cross-wine and the position of max. darkness will tell the vibr. dir of the polarizer. In Case of tourmaline the lighest colour will tell about the Vibration dir. of the polarizer. Sign of the mineval. E along the vad ip te substraction (-ve) sign 0 550 Ολ 1100 2x isbwkay. (tue) sign. 1650 3 path difference of order=nd extinction. path differena (n+1) X brightness Approximate radi of the circles corresponding to retardation of 2x,3x,4x, ηλ aret 112r, JBM, Jur No of isochromes & Birefringence (High Birefringence possess More BAO ischiomes than the low Bivefriyena No of ischiomes a thicknest (more thick isochromes, nore To obscure the interference figy use the Bert van lens or remove the numerical aperture of the objective used, the wider the angle of the con of light from the crystal that enters the objective. Melatope means the position of the O.A and not the intusection of the cross-wires, Biaxial Minerals -->. Thicker than uniaxial minerals **Bxa actue bisectrix. (2V<45°) (zorx).** In BXO → obtuse bisectrix melatopes will be outside the field of view. Diff. btw-Uniaxial & Biaxial - The isogyres will be significantly thinner than the other one. (Zorx) Just by looking. we can not tell about the central line (axis), ie whethaitis the z axis or X-axis. -> Z will be the BXA. acterte Bisectrix, In Alkaline Hbl, as "No in creaser, the yellow colour of the Hbe varnishes and becomes green. If Na' content in any mineral increases colour becomes good. If there is only one isogyre and on rotation it parse through the intersectin "Cross wive & become II to one of the cross wire, In that case we can not determine thout whether the optic figure is Biaxial or uniaxial." - Highly curve Biaxial mineral - Lightly curve isogyre → Uniaxial. mineral, Aeqerine, Glaucophane, Rie beckiter they have more or less same epti colour, pleochroism, Other properties, pleochroism- light green, dark green, light blue-dark blue we determine the '2' angle and then we determine the refractive indices and for&R.I we need the vibration direction. { Circular Section से is determine karte है Principle " " " } In Conoscopic, If we get Centresd O. A, then we wil have the circular Section of the tetragonal, crystal system Now go back to the orthoscopic arrangemett to get the R.I. Off Centred O. A fig. sirf Uniarid में होती है या Biaxial में? How to find R.I? < Oblique Illumination (In Orthoscopy? Becke-line Method 7. - Take a mineral - use TIR CTotal internal Reflection - So that the boundary is visible) - Close the diaphragm - Raise the tube or lowi the Stage. - Blurredness increases of the boundary Becke line - Becke line moves towards the high R.I mineral - We use liquids of knoww R.I, we can precisely determine the R.I Staining It is a v. simple technique by which every mineral cam be identified It requires certain chemicals Chiefly used in sedi mentary rocks Especially for K-Feldspars (orthoclase), Anorthoclase) are difficult to identify in microscope. Cordierite is Sometimes mistakem for plagioclase. 'Plagiadase forms by magmatic differentiation). Staining is based on visual interpretation. It is also used for the ichuntification of the Carbonates. (limestones). Staining is always preceded by Etching. Etching is the roughness of the surface of the mineral So that the minerale Can readily react with the Stain Ichemicals. Etching can be done by two acids 52% HCG- for all sort of Carbonates 52% HF for all the silicate minerals HF is the best etching agent. Etching can be done using the slides but the rock showd not be covered by the Coverslip. If the Mock is very porous, we use on additional adhesive paraffin, (lake side cement, epoxy, resin) (used under especial Conditions). (paraffin is used. for porous rocks.) AX hos to be A bottle filled with HF, is left open and the slide is kept upside down over the opening of the HF bottle. Eq. Gvanite = K. Feldspar + Plagiodase. Feldspar + Quartz. For staining we need→(ⅰ) Ball₂ (ii) Sodium Cobaltinit rite (iii) Rhodhizonic Acid. Method->. - Rinse the etched mineral with water. - Immerse in BaCl₂ Sot" for 2-3 times. - Re-Rince. - Immerse it in Sodium Cobaltinitrite stor sot". - If we yst get light yellow colour. - This means the mineral is K. Feldspar. - Now, deanly wash the mineral and rime it into the Rhodhizonic acid sol. - If we get brick red spot Colour. The mineral is Plagioclase Feldspar. - The unstained part of the vock is Ka Quartz (N.Sta - Quartz can never bestained by any combination of reagent If the plag. is pure albite it will not give brick red colour there has to be atleast 3% anorthite to get a brick red colour. For Orthoclase & others.. - Wash the slide and put the slide over 80°C, So that it becomes a bit gong powdery for gercy. - Cool it and vince it in Call, soi" (acts as a Catalyst for stain) and then BaCl, Sot" and then Na Cobaltinitrite sot" and dry the Sol". - Light Grey - plagioclase - Umstained Quartz - Light yellow Orthodave. Plagioclase Anorthoclase Sat (untwinned plagiodase) (ordierite Eg. We we Amain th Solution → We go tile Sodium Cobaltinitrite Stage we have to rinse it with wate & dip it into BaCl2 and then again rinse it and then we dip it into Amaranthson. Then, if - Light Red Plagiodase. - Greyish Cherry Red Anorthoclase - Deep Red Cordierite. Sanidine does not respondiumstantin Amaranth sol". The that part is Sanidine Pure Albite is also unstaind. Carbonates. Etching & done with cold dil. HCl. Brisk effervescence, dragonite, Calcite, or witherite. No effervescence -, all other carbonates. Do etching with hot Hce for 1 to 3 min Now we need different sol's- - Alizarine Red S - FEIGL'S Sol" - Rhodizonic Sol" - MAGNESON - TROPAEOLINOO - Potassium Ferricynide - Potassium Hydroxide - Ammonium Sulphide & Copper Sulphate. ARS. (EFARS) An etched mineral is put in ARS. We get 3 colours. - Purple Stains → - Deep Red Staine -> - No colour For purple E+ ARS + 30% NaOH and boil - Dark Purple. Ankerite - Douk Red Brown Cerrusite - No Color Strontianite (Revats to colourless mineral). Cie Purple turns coloculess mineral). Deep Red Stains - Now apply FEIGL'S SOL". - Black. Anhydrite Aragonite - Colorless / No Colour. If Colorless it has to be treated with 30% NaOH+bål - Purple Colon High: Mg - No Colour - it has to be treated with Rhodizonic sol" - Orange Red - witherite - NC E+ ARS → NColour Treat with 30% NaOH and boil. No cobur (Anhydrite) Dark Brown (Siderite). Purple (5% NaOH + boil) No Colour (NC). (Treat with Benzine). Deep Blue (Magnesite or Gypsum) NC (Smithsonite) (Troppeolin 00+ 1.5% H2S04+12%. Ferricyanide) Chemical Analysis, Analysis Point Secondary Rad", Excited e remains let's own orbit. Backscattered Rad" energy reflectid back Characteristic Rad" energy exites the é so that it leaves it's orbit and jurop to higher level. ==End of OCR for page 25==