Agate banding

Figure 10.18. Schematic illustration of textures seen in a geode. (1) Agate banding (including (2) Rundelbundlung) (3) larger crystals (4) Uruguay band.

Figure 10.19. (a) Polarizing photomicrograph of agate banding, (b) Transmission-type electron photomicrograph [16]. 

Band, m. volume binding.—n. band ribbon, tape, strap, strip, belt, hoop hinge bond, tie, ligament, -achst, m. banded agate, ribbon agate. 

Agate Waxy Translucent Banded Irregular, sometimes circular bands... 

Potassium iodide (830 mg, 5.0 mmol) was finely ground in an agate mortar and the diazonium salt 292 (0.50 mmol) added in five portions and coground for 5 min each. After a 24-h rest with occasional grinding, the diazonium band in the IR spectrum had completely disappeared. The potassium salts were removed by washing with cold water. The yield of pure aryl iodide 295 was 100% throughout (Scheme 44). 

The barbituric acid derivative 40a-f (0.50 mmol) was ground in an agate mortar. Solid diazonium salt289j (0.50 mmol) was added and coground in five portions for 5 min each. Most of the diazonium band at 2280 cm had disappeared, but completion of the reaction was achieved by 24 h ultrasound application in a test tube. After neutralization (0.5 N NaOH, 20 mL), washing (H2O), and... 

Figure 8.3. Examples of banding patterns formed by geometrical selection in (a) malachite (b) rhodochrosite (c) agate.

If two individuals conjugate on an r or a z face, a nucleus of a Japanese twin with 1122 as the composition plane is formed. This indicates that a Japanese twin is not a penetration twin (i.e. not the upper half of an X-shape), but a contact twin (i.e. the upper half of a Y-shape). Horizontal banding in geode agate (see Section 10.9) appears through grain size variation due to gravitational sedimentation, and con-... 

AGATE. Agate is a variety of chalcedony, whose variegated colors are distributed in regular bands or zones, in clouds or in dendritic forms, as in moss agate. 

Onyx is a variety of agate in which the parallel bands are perfectly straight and can be used for the cutting of cameos. Sardonyx has layers of dark reddish-brown carnelian alternating with light and daik colored layers of onyx. 

Onyx is a striped variety of the common silicate mineral called agate, with alternating black and white bands. It comes mainly from India and South America. Sardonyx is a variety of onyx with brown and white bands. 

The pellet (pressed-disk) technique depends on the fact that dry, powdered potassium bromide (or other alkali metal halides) can be compacted under pressure to form transparent disks. The sample (0.5-1.0 mg) is intimately mixed with approximately 100 mg of dry, powdered KBr. Mixing can be effected by thorough grinding in a smooth agate mortar or, more efficiently, with a small vibrating ball mill, or by lyophilization. The mixture is pressed with special dies under a pressure of 10,000-15,000 psi into a transparent disk. The quality of the spectrum depends on the intimacy of mixing and the reduction of the suspended particles to 2 gm or less. Microdisks, 0.5-1.5 mm in diameter, can be used with a beam condenser. The microdisk technique permits examination of samples as small as 1 fxg. Bands near 3448 and 1639 cm-1, resulting from moisture, frequently appear in spectra obtained by the pressed-disk technique. 

An agate is banded microcrystalline quartz (chalcedony). The bands are curved, and can be any color, opaque or translucent. 

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