Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Common opal

Opal is a common mineral in chemical sediments, as deposits around hot springs, replacing fossils such as wood, or as secondary vein-filling. Most opal is common opal, without the internal play of colors that makes some opal precious. Common opal is usually light colored, and has a distinctive waxy luster. [Pg.26]

Hot springs may contain lots of different minerals in solution. Upon reaching the surface, these waters cool off and the compounds held in solution will precipitate around vents or pools. The most common deposits around hot springs are composed of calcite or common opal. Both of these minerals are colorless when pure, but are often colored by other materials in the water. Oxides of iron are the most common pigments in these situations. In shades of brown, red, and yellow, iron oxide may color an entire deposit, or appear episodically, dyeing some layers and not others. [Pg.45]

Other examples are common opal or fire opal. A key component of opal is the included water, which is typically present in 3-9 wt% but may be as much as 20wt%. It is a little tricky to polish opal (a fine example is shown in Figure 36.24), partly because you must not remove the water and partly because it is quite soft. Opal thus has much in common with chalcedony, another form of fine-grain quartz. [Pg.666]

The parameter e0 was chosen for best agreement with the experimental data of Opal et al.52 at = 500 eV. Jain and Khare applied this equation to the calculation of ionization cross sections for C02, CO, HzO, CH4, and NH3 and achieved fairly good agreement with experiment for all cases except for CO, where the cross section was too low, though the ionization efficiency curve still exhibited the correct shape. The main limitation of this method, which it has in common with the BED theory, is the inclusion of the differential oscillator strengths for the target molecule which restricts the number of systems to which it can be applied. [Pg.333]

Figure 5. Abundance of opal phytoliths as summarized from original petrographic data. Key 0, absent R, rare C, common and A, abundant. Sample coordinates same as in Figure 3. Note essential absence of phytoliths in the Sierra units 1 and 2 (Palenque), and 7 (Xupa orientation). Figure 5. Abundance of opal phytoliths as summarized from original petrographic data. Key 0, absent R, rare C, common and A, abundant. Sample coordinates same as in Figure 3. Note essential absence of phytoliths in the Sierra units 1 and 2 (Palenque), and 7 (Xupa orientation).
Silicon dioxide (SiO ) is the most abundant compound in the Earths crust. Known as common sand, it also exists in the forms of quartz, rock crystal, amethyst, agate, flint, jasper, and opal. It has many industrial uses. [Pg.197]

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... [Pg.118]

The major aluminous clay minerals, alkali zeolites and feldspars which are most commonly associated in nature can be considered as the phases present in a simplified chemical system. Zeolites can be chemiographically aligned between natrolite (Na) and phillipsite (K) at the silica-poor, and mordenite-clinoptilolite at the silica-rich end of the compositional series. Potassium mica (illite), montmorillonite, kaolinite, gibbsite and opal or amorphous silica are the other phases which can be expected in... [Pg.122]

About twenty different skeletal minerals are reported from organisms7,8 however, only four are common (1) aragonite, (2) calcite, (3) dahllite = carbonate hydroxyapatite, and (4) opal. The remaining minerals depicted in Fig. 1 are either trace constituents or occur only in a few isolated species. It is for this reason that the article concentrates on carbonate, phosphate and silica deposition in plants and animals. For reviews on general aspects of biomineralization and discussions on individual taxonomic classes see Ref.9-47 ... [Pg.4]

Figure 9. Picosecond photoluminescence maps of opal CT (left pannel) and opal A (right pannel). The PL intensity z is plotted in logarithmic scale and increases from blue colors to red colors. Zero-time delay corresponds to the beginning of the streak camera sweep. Opal CT "common" is from Mapimi, Mexico opal A "noble" is from Lightning Ridge, Australia. Figure 9. Picosecond photoluminescence maps of opal CT (left pannel) and opal A (right pannel). The PL intensity z is plotted in logarithmic scale and increases from blue colors to red colors. Zero-time delay corresponds to the beginning of the streak camera sweep. Opal CT "common" is from Mapimi, Mexico opal A "noble" is from Lightning Ridge, Australia.
Silicon dioxide. Because silicon dioxide is so readily available in nature, there is only infrequent need to produce this compound in either the laboratory or the plant. Many familiar materials consist of silicon dioxide (or silica) in varying degrees of purity. Thus, flint, agate, amethyst, quartz, onyx, opal, granite, petrified wood, sand, and sandstone are all materials that consist entirely or largely of silica. You may recognize that all these materials have a variety of common uses and should recall, from preceding discussions, cases in which silicon dioxide is used in certain commercial chemical processes. [Pg.592]

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. [Pg.153]

Play of color is the term used to describe the internal spectral colors that appear inside some specimens of materials like opal and some synthetics. The colors seem to move when the specimen is turned or the light source is moved. Labradorescence is a broad play of colors common in labradorite and other minerals (mostly feldspars) having polysynthetic twinning. [Pg.12]

Opalescence is a pearly or milky internal reflection, most common in white or light-colored minerals such as some opal or moonstone (albite or ortho-clase feldspar). This is also known as adularescence. Like iridescence and play of color, these properties are not consistent within any natural material, and can only be used to describe individual specimens. Some synthetic materials have been created specifically to display these properties and so always show them. [Pg.12]

Diatoms are single-celled algae that produce a hard skeleton made of hydrous silica (opal). The rock that forms from consolidated layers of diatom skeletons is called diatomite. This material has many common and commercial names, including diatomaceous earth, Fuller s earth, kieselgur, and tripo-lite. Diatomite is mined and used as building material, in filters, as insulation, as a mild abrasive, and as a filler in dry chemicals. [Pg.46]

JLm diameter spheres, called lepispheres, which are composed of bladed crystals 30-50 nm thick. Kastner et al. (1977) reported that the formation of opal-CT results from dissolution followed by reprecipitation reactions that require a source of magnesium, alkalinity, and hydroxide ion. The presence of aluminosilicate phases commonly retards the formation of opal-CT (Hinman, 1998). [Pg.3561]

Silica biomineralization is the incorporation of the extremely fine-grained, and virtually amorphous varieties of opal, a hydrated form of the common, but highly insoluble species that has the formula Si02 H20 (see Section 8.05.2.2.1). [Pg.4011]

Opal is related to the very common Si02 mineral species, quartz. Oceans are at present undersaturated with respect to opal (Broecker, 1971) possibly because of the biological formation of animals with silicified skeletons such as the diatoms. These delicate structured creatures, which proliferate in the upper photic zone, dissolve at depth. Therefore, only robust siliceous skeletons such as sponge spicules are retained in sediments that accumulate in deep waters, although some diatoms survive on the continental shelf under zones with high productivity. The initial deposition of the amorphous hydrated silica, opal, converts first to opal-CT and eventually to crystalline quartz (Kastner, 1981). [Pg.4011]


See other pages where Common opal is mentioned: [Pg.1152]    [Pg.374]    [Pg.581]    [Pg.1152]    [Pg.374]    [Pg.581]    [Pg.290]    [Pg.424]    [Pg.26]    [Pg.26]    [Pg.212]    [Pg.211]    [Pg.27]    [Pg.73]    [Pg.404]    [Pg.323]    [Pg.12]    [Pg.58]    [Pg.106]    [Pg.123]    [Pg.134]    [Pg.290]    [Pg.187]    [Pg.196]    [Pg.108]    [Pg.421]    [Pg.256]    [Pg.22]    [Pg.163]    [Pg.2949]    [Pg.3553]    [Pg.3554]    [Pg.3566]    [Pg.4007]   
See also in sourсe #XX -- [ Pg.26 ]




SEARCH



Opals

© 2024 chempedia.info