Acicular crystals

Aminophenol. This compound forms white plates when crystallized from water. The base is difficult to maintain in the free state and deteriorates rapidly under the influence of air to pink-purple oxidation products. The crystals exist in two forms. The a-form (from alcohol, water, or ethyl acetate) is the more stable and has an orthorhombic pyramidal stmcture containing four molecules per unit cell. It has a density of 1.290 g/cm (1.305 also quoted). The less stable P-form (from acetone) exists as acicular crystals that turn into the a-form on standing they are orthorhombic bipyramidal or pyramidal and have a hexamolecular unit (15,16,24) (see Tables 3—5). 

Mfldelchen, n, little needle (or pin), I adel-eisenerz, n., -eisenstein, m. needle iron ore (gdthite in acicular crystals), -erz, n, needle ore (aikinite in acicular crystals), -faser, /, acicular fiber. nadelfSrmig, a. needle-shaped, acicular. Madel-holz, n. conifers (collectively), esp, pines and firs wood of conifers, soft wood, -holzer, n.pl. (Bot.) Finales, Coniferae, -holzkohle,/. soft-wood charcoal, -holzteer, m, soft-wood tar, (loosely) pine tar. -holzzellstoff, m. cellulose (or pulp) from conifers, nadelig, a. needly, acicular. 

C27H45OH, crystallising in the form of acicular crystals and found in all animal fats and oils, in bile, blood, brain tissue, milk, yolk of egg, the medullated sheaths of nerve fibres, the liver, kidneys and adrenal glands. 

Microscopically, the crystal type depends on the method of preparation of halcinonide. Slabs, either 2 to 4, 5 to 10, or 10 to 15 microns square, were found in three lots of halcinonide, intermingled with needle-like (acicular) crystals 5 to 10 microns long.27... 

In his recent book, Dietrich (1985) described the common habits of tourmaline as being acicular, filiform, asbestiform, and chalcedonylike, and as whiskers. This last term indicates that tourmaline composition fibers have been synthesized. The wide range of forms for minerals in this group probably accounts for some of the early confusion when samples of tourmaline were equated with asbestos. Schorl, now known to be NaFe Al6(B03)3Si60ig(0H)4, usually occurs as dark green or black acicular crystals. Based on their appearance alone, schorl could easily be mistaken for an amphibole. 

Fig. 4.20 Synthetic hematites grown from ferrihydrite at temperatures <100°C (Schwertmann, unpubl.) a) Hexagonal plates grown at pH 7 and RT acicular crystals are goethite b) Laths grown at pH 11 and 80 °C in the presence of 2.5 10 M citrate (see Schwertmann et al., 1968). The fine granular material is unreacted ferrihydrite c) Framboids grown at pH 6 and 70°C in the presence of 2 10 M oxalate (see Fischer, ...

Rheological studies involving Fe oxides appear to be sparse. Most are carried out on acicular crystals, usually maghemite. Details of the method of synthesis or properties of the particles are often lacking. 

Fig. 16.7 Electron micrographs of soil goethites. a) Acicular crystals from an Oxisol on peridotite. New Caledonia (Schwertmann, Latham, 1986 with permission), b) Starlike crystals from a redoximorphic paddy soil, China, c) Irregular crystals from an Ultisol on basalt, South Brazil (see also Schwertmann, Kampf,...

Subsequent reaction of the monosulfate with gypsum produces acicular crystals of ettringite. Monosulfate apparently does not contribute to expansion, whereas the formation of ettringite involves expansion. A recently issued patent [75] covers the use of prehydrated high-alumina cement (H-HAC), lime and gypsum mixtures. Particle type, size, thickness of protective coating, and presence of moisture determine the rate and extent of expansion [Fig. 6.11]. 

Precipitation of ferric hydroxide gel was also observed in the preparation of spindlelike hematite (a-Fe203) particles in a dilute ferric chloride solution in the presence of phosphate (9). In this case, however, the positive role of the gel was not definite since similar uniform hematite paricles were obtained as well in homogeneous systems in the presence of the same anions (9). Also, Hamada and Matijevic (10) prepared uniform particles of pseudocubic hematite by hydrolysis of ferric chloride in aqueous solutions of alcohol (10-50%) at I00°C for several days. In this reaction, it was observed that acicular crystals of (3-FeOOH precipitated first, and then they dissolved with formation of the pseudocubic particles of hematite. The intermediate P-FeOOH appears to work as a reservoir of the solute to maintain an ideal supersaturation for the nucleation and growth of the hematite. Since the (3-FeOOH as an intermediate and the pseudocubic shape tire not peculiar to the alcohol/water medium... 

Description-. Colourless, acicular crystals with characteristic sweet and acrid odour (Budavari, 1996)... 

Small, yellowish, acicular crystals, soluble in about 300 parts of cold water. Silver nitrite is more readily soluble in hot water, but suffers partial decomposition therein. 

Microscopic evaluation of the crystals grown in seeded systems indicates that the single crystals of seed grow only partially, and new acicular crystals are grown separately from the seed crystals (Figure 5). Since... 

Arsenic trichloride may be solidified by cooling. It forms white, nacreous, acicular crystals of melting point -16° C. The solidification is accompanied by an appreciable decrease in volume. 

CHRYSOCOLLA. This mineral, a hydrous silicate of copper probably corresponding to the formula CuiHiSiiOstOHjj. is perhaps a mineral gel, for it usually appears as an amorphous mass, in veins, or as incrustations. Common occurrence as massive cryplocrysiallinc character, possibly orthorhombic extremely rare as small acicular crystals. 

Rutile is found as an accessory mineral in many kinds of igneous rocks, and to some extent in gneisses and schists. In groups of acicular crystals it is frequently seen penetrating quartz as the filches d amour from Grisons, Switzerland, and Brazil. Rutile is found also in Austria, Italy, Norway, South Australia, and Brazil. In the United States it occurs in Vermont, Massachusetts, Connecticut, New York, Pennsylvania. Virginia, Georgia, North Carolina, and Arkansas. 

ULEXITE. This mineral, a hydrated borate of sodium and calcium. NaCaBsOg 8H2O, is a product of crystallization in arid regions from shallow playas and lakes. Ulexite crystallizes in the tridinic system, but usually occurs in rounded masses of line-libered acicular crystals. The hardness is 2.5. specific gravity, 1.96, silky luster and white color. The mineral is found abundantly in Chile and Argentina and in Nevada and California in the United States. Ulexite is a source of boron. 

Yield.—Almost theoretical (32 gms.). Red acicular crystals insoluble in water somewhat soluble in warm petroleum ether M.P. 71° sublimes on heating. (A., 204, 251 215, 134.)... 

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