Minerals, refractive indices

These materials are rocks (mixtures of minerals). Refractive index, hardness and density for these materials are for the most common or principle constituent mineral. Properties of individual specimens may vary widely from these values. 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

Methylene iodide [75-11-6], CH2I2, also known as diio dome thane, mol wt 267.87, 94.76% I, mp 6.0°C, and bp 181°C, is a very heavy colorless Hquid. It has a density of 3.325 g/mL at 20°C and a refractive index of 1.7538 at 4°C. It darkens in contact with air, moisture, and light. Its solubiHty in water is 1.42 g/100 g H2O at 20°C it is soluble in alcohol, chloroform, ben2ene, and ether. Methylene iodide is prepared by reaction of sodium arsenite and iodoform with sodium hydroxide reaction of iodine, sodium ethoxide, and hydroiodic acid on iodoform the oxidation of iodoacetic acid with potassium persulfate and by reaction of potassium iodide and methylene chloride (124,125). Diiodoform is used for determining the density and refractive index of minerals. It is also used as a starting material in the manufacture of x-ray contrast media and other synthetic pharmaceuticals (qv). 

Dispersion staining is useful for rapid deterrnination of refractive index and dispersion. It is appHed most often, however, for needle-in-a-haystack detection of any particular substance in a mixture such as chrysotile in insulation, cocaine in dust samples, quartz in mine samples, or any particular mineral, eg, tourmaline, in a forensic soil sample. 

Chemical modification of the wax can improve smear resistance (5). Sihcones, which do not harm furniture finishes (6), are incorporated as film-forming ingredients in furniture pohshes. The lubricant properties of sihcones improve ease of apphcation of the pohsh and removal of insoluble soil particles. In addition, sihcones make dry films easier to buff and more water-repeUent, and provide depth of gloss, ie, abihty to reflect a coherent image as a result of a high refractive index (7). Wax-free pohshes, which have sihcones as the only film former, can be formulated to dehver smear resistance (8). Another type of film former commonly used in oil-base furniture pohshes is a mineral or vegetable oil, eg, linseed oil. 

The mineral talc is extremely soft (Mohs hardness = 1), has good sHp, a density of 2.7 to 2.8 g/cm, and a refractive index of 1.58. It is relatively inert and nonreactive with conventional acids and bases. It is soluble in hydroduoric acid. Although it has a pH in water of 9.0 to 9.5, talc has Lewis acid sites on its surface and at elevated temperatures is a mild catalyst for oxidation, depolymerization, and cross-linking of polymers. 

The disadvantage of this procedure is that the minerals maybe physically or chemically altered during burning. Eor example, the refractive index of clay minerals is changed the color, birefringence, and pleochroism of micas is altered carbonates are destroyed and the iron sulfides are oxidized to iron oxides. 

Petroleum or mineral oil (kerosene, etc.) are less soluble in alcohol than most oils. They have a low specific gravity and refractive index, and are not saponified by alcoholic potash. The lower boiling fractions can usually be detected by their odour, and the higher boiling fractions remain in the residue on fractional distillation. They are unaffected by fuming nitric acid. 

Uses Determining refractive index of minerals paint diluent dyed hexane is used in thermometers instead of mercury polymerization reaction medium calibrations solvent for vegetable oils alcohol denaturant chief constituent of petroleum ether, rubber solvent, and gasoline in organic synthesis. 

As a pigment, each iron oxide has an optimum particle size which is that with the maximum scattering cross section. This optimum particle size is lower, the higher the refractive index of the mineral. For hematite, the size corresponding to the maximum in scattering/absorption cross section is ca. 1 pm. As the particle size decreases, the relative scattering cross section drops to zero and the relative absorption cross section levels out. As a result, very small particles of hematite are transparent. 

White powdery solid (rhombic plate) the mineral berhnite (AIPO4) has hexagonal quartz-like structure refractive index 1.546 mp > 1,500°C density 2.566 g/cu insoluble in water and alcohol Ksp 9.83x10 ° very slightly soluble in HCl or HNO3. 

White powder refractive index 1.47 density 2.71 g/cm mp 770°C (decomposes) hygroscopic readily soluble in water (31% at 0°C solubihty increases with temperature 98% in boiling water) soluble in dilute mineral acids slightly soluble in alcohol. 

Monohydrate, Ba(0H)2 H20 is a white powder density 3.743 g/cm shght-ly soluble in water soluble in dilute mineral acids. Octahydrate, Ba(0H)2 8H20 is a colorless monoclinic crystal density 2.18 g/cm at 16°C refractive index 1.50 melts at 78°C vapor pressure 227 torr loses seven molecules of water of crystallization when its solution is boiled in the absence of atmospheric CO2 forming solid monohydrate further heating produces anhydrous Ba(OH)2 melting at 407°C readily dissolves in water (3.76 g/100 g at 20°C and 11.7 g/100 g at 50°C) aqueous solution highly aUtahne also soluble in methanol shghtly soluble in ethanol insoluble in acetone. 

Soft crystalline solid rhombic crystal pure salt is white but color may vary the color of the mineral barite may vary among red, yellow, gray or green depending on impurities density 4.50 g/cm refractive index 1.64 melts around 1,580°C decomposes above 1,600°C hardness 4.3 to 4.6 Mohs insoluble in water (285 mg/L at 30°C) and alcohol Ksp 1.1 x 10-i° soluble in concentrated sulfuric acid. 

White cubic crystal or powder refractive index 1.434 density 3.18 g/cm hardness 4 Mohs melts at 1,418°C vaporizes at 2,533°C insoluble in water (16 mg/L at 20°C) Ksp 3.9xl0 ii slightly soluble in dilute mineral acid soluble in concentrated acids (with reaction). 

White cubic crystal which turns blue when heated at 178°C density 4.14 g/cm the mineral nantokite (CuCl) has density 4.14 g/cm , hardness 2.5 (Mohs), refractive index 1.930 melts at 430°C becoming a deep, green hquid vaporizes around 1,400°C vapor pressure 5 torr at 645°C and 400 torr at 1,250°C low solubihty in water (decomposes partially) Ksp 1.72x10 insoluble in ethanol and acetone soluble in concentrated HCl and ammonium hydroxide. 

White powder cubic crystals the mineral marshite is a red-brown crytal density 5.67 g/cm refractive index 2.346 hardness 2.5 Mohs melts at 606°C vaporizes around 1,290°C insoluble in water and dilute acids soluble in aqueous solutions of ammonia and alkali salts of cyanide, iodide and thiosulfate ions. 

The tetrahydrate of the tribasic phosphate, Mg3(P04)2 4H2O is a bulky and soft white powdery material monochnic crystals density 1.64 g/cm at 15°C slightly soluble in water (0.2 g/L at 20°C) soluble in acids. The naturally occurring octahydrate, bobierite, is a white crystalline solid, containing monoclinic plates refractive index 1.510 density 2.195 g/cm at 15°C loses three molecules of water of crystallization at 150°C loses all water at 400°C insoluble in water soluble in dilute mineral acids. 

The monohydrate MgS02 H20, as the mineral kieserite, consists of colorless monoclinic crystals refractive index 1.523 density 2.445 g/cm becomes anhydrous on heating at 200°C soluble in water. 

Zinc sulfide is white to gray-white or pale yellow powder. It exists in two crystalline forms, an alpha (wurtzite) and a beta (sphalerite). The wurtzite form has hexagonal crystal structure refractive index 2.356 density 3.98 g/cm3 melts at 1,700°C practically insoluble in water, about 6.9 mg/L insoluble in alkalis soluble in mineral acids. The sphalerite form arranges in cubic crystalline state refractive index 2.368 density 4.102 g/cm changes to alpha form at 1,020°C practically insoluble in water, 6.5 mg/L soluble in mineral... 

Irradiation by fast neutrons causes a densification of vitreous silica that reaches a maximum value of 2.26 g/cm3, ie, an increase of approximately 3%, after a dose of 1 x 1020 neutrons per square centimeter. Doses of up to 2 x 1020 n/cm2 do not further affect this density value (190). Quartz, tridymite, and cristobalite attain the same density after heavy neutron irradiation, which means a density decrease of 14.7% for quartz and 0.26% for cristobalite (191). The resulting glass-like material is the same in each case, and shows no x-ray diffraction pattern but has identical density, thermal expansion (192), and elastic properties (193). Other properties are also affected, ie, the heat capacity is lower than that of vitreous silica (194), the thermal conductivity increases by a factor of two (195), and the refractive index, increases to 1.4690 (196). The new phase is called amorphous silica M, after metamict, a word used to designate mineral disordered by radiation in the geological past (197). 

The refractive index is the most important optical property and its effect in determining the appearance of the polymer composite has already been referred to above. Amorphous fillers such as glass fibres and beads have only one refractive index, but most mineral fillers are crystalline and have anisotropic crystal structures resulting in a number of different indices, and this can cause complex and undesirable interference effects [27]. 

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