Black opal

Black Opal With Brilliant Vivid Colors. Smithsonian Gem and Mineral Collection,... 

Opal is a hydrous silica (Si02), sometimes thought of as an amorphous silica gel. It is a fairly soft gem, measuring only 5 to 6 on the Mohs scale. It is relatively common in nature except in its precious form, which comes mainly from Australia. In Switzerland, since 1970, opal of precious quality has been made synthetically. Usually cut in the cabochon shape to permit its rainbowlike display of color, opals come in white, black, and fire varieties. Black opals are dark gray to blue, and fire opals, which are more transparent than other opals, are usually orange-red in color. 

Black opal Flashes and speckles appear against black background... 

Opal in which brilliant colors appear against a dark background are the most valuable and probably the least understood. The effect is not entirely that of a dark substrate but may also involve a phenomenon similar to that of a light trap like a bundle of needles viewed from the points. There are no doubt other effects as well, such as a dark material scattered through the matrix. For example, black opals were examined by Mitsyuk et al. (357). The dark organic material in the pores was found to resemble a hydrocarbon. After calcination the decolorized opal- increased in density from 2.0 to 2.2 g cm as organic matter and water were removed. The microstructure of opal has been described in further detail by Sanders and Darragh... 

This synthesis was announced in 1967 (396). Since then synthetic opals have become available from Gilson of Switzerland (397). These have the appearance of natural opal and many of the same properties, for example hydrated, density 2.113, refractive index 1.45, singly refractive, amorphous, hardness 6.15 mohs (398). The synthetic black opal is said to be indistinguishable from the natural ones by visual examination. Some difference in fluorescent properties was reported. The method of manufacture is a trade secret of the manufacturing company, Gilem S. A. 

Composite Gemstones. Many types of composite or assembled gemstones have been made (1). Some are shown in Figure 3. In the United States a doublet has two pieces combined using a colodess cement. If three pieces are used, or if two pieces are assembled using a colored cement, the gemstone is a triplet. The use of composite stones has declined rapidly with the rise of inexpensive synthetics. Frequendy seen are opal doublets, where precious opal is backed by a black material. In opal triplets a thin sHce of precious opal is cemented between a black backing and a clear cover, usually of quartz. Additionally, insects and even fish have been inserted into amber. 

Precious opal is usually defined by the background color, black, white, or fire (orange). There are terms used to describe the distribution of the internal colors, and which colors are dominant. 

Figure 15 Alternating paleoenvironments of desert CAM shrublands and C3 grasslands represented by a sequence of Quaternary paleosols (0-100 ka) in the Palouse loess near Kahlotus, Washington, USA showing (left to right), field section with thermoluminescence dates and paleosol identification (Moll, is Mollisol, Arid, is Aridisol), paleosol position and development (represented by black boxes), paleosol calcareousness (scale based on acid reaction), Munsell hue (measured dry in field), sand-silt-clay proportion, of pedogenic carbonate, of opal phytoliths, abundance of earthworm pellets, and abundance of cicada burrows (source Retallack, 2001c).

A combination of several different opaline materials may be found juxtaposed. For example, in fossilized wood both tridymite and crystobalite may be determined in a sample whde adjacent portions of the sample may be composed of opal-A. The silicified wood may be transparent or translucent, clear and colorless, or white, yellow, red, brown, and black, indicating inclusions of other, usually iron-containing, complexes during precipitation of the colloid or gel. The faithfully preserved structures of fossilized wood suggest that the replacement phenomena are molecule-by-molecule processes that take place under low temperamres and pressures, and require concomitant removal of nonsiliceous compounds but do not disrupt the ceUularity of the woody tissues. Alternatively, primary... 

Favorable Colors Dark reds and black Lucky Gem Opal... 

Figure 2. Slender crystals of clinoptilolite in pseudo-morphic pore of a glass shard which is fringed by mont-morillonite ana opal. Some void (grey-black) remains.

Fig. 2, 20 TEM-pictures of multiphasic materials (a) Micromorphology of high impact polystyrene. White Polystyrene, black Polybutadiene (see Sect. 5.5.2.4). (b) Lamellar micromorphology of an AB diblock copolymer (see Sect. 3.4.2.1). (c) Quasi crystalline order of polystyrene particles in an artificial opal ...

Fig. 1. Selected dynamin family members in mammals. The three dynamin family members that have been studied in our lab are shown here. Dynamin is involved in vesicular traffic. Drpl contributes to mitochondrial outer membrane division. Opal is localized to the mitochondrial intermembrane space where it affects inner membrane morphology and mitochondrial fusion. All family members have GTPase, Middle, and Assembly domains. Genuine dynamins have a pleckstrin homology (PH) domain and a C-terminal proline rich domain (PRD). Other family members have divergent segments at the N-terminus (Opal) or between the middle domain and GED (black areas in Drpl and Opal). The N-terminus of Opal has a predicted mitochondrial targeting sequence and coiled coil.

A polymer gel based on an (inverse) opal was applied in order to obtain shorter switching times, which are also desirable for electrochemical color display purposes [346]. Hence, an all-color display was developed that, dependent on the applied potential, could reversibly switch between blue, green, red, and black. Here, crosslinked polyferrocenylsilane gels were partly swollen with glutaronitrile electrolyte. The degree of swelling was controlled electrochemically. Subsequently, the distance between the voids formed by the silica beads, which were etched by hydrofluoric acid treatment, could be altered. It should be mentioned that there are also other concepts for electrically switchable photonic crystals that are not directly connected to electrochemically induced solvation [347-349]. 

Figure 3.42 SEM images of the templated inverse-opal TiOi films (a, b) from 1000 nm polystyrene (c, d) from 400 nm polystyrene and (e,f) from 240 nm polystyrene microspheres. The three black spots within the hexagons indicated in (b) show the holes connecting the spherical cavities to the inner layer. Adapted from Kwak et al., 2009 . Copyright (2009) Wiley-VCH Verlag GmbH 8c Co. KGaA...

---