Spherulization

Examples are provided by the work of Carman and Raal with CF2CI2 on silica powder, of Zwietering" with nitrogen on silica spherules and of Kiselev" with hexane on carbon black and more recently of Gregg and Langford with nitrogen on alumina spherules compacted at a series of pressures. In all cases, a well defined Type II isotherm obtained with the loose powder became an equally well defined Type IV isotherm with the compact moreover both branches of the hysteresis loop were situated (drove the isotherm for the uncompacted powder, but the pre-hysteresis region was scarcely affected (cf. Fig. 3.4). The results of all these and similar... 

Collection. IDPs can be coUected in space although the high relative velocity makes nondestmctive capture difficult. Below 80 km altitude, IDPs have decelerated from cosmic velocity and coUection is not a problem however, particles that are large or enter a very high velocity are modified by heating. Typical 5-)J.m IDPs are heated to 400°C during atmospheric entry whereas most particles larger than 100 ]Am are heated above 1300°C, when they melt to form cosmic spherules (Pig. 6). 

Pig. 6. A 0.3-mm-diameter cosmic spherule coUected from the ocean floor. The particle is composed of oUvine, glass, and magnetite and has a primary element composition similar to chondritic meteorites for nonvolatile elements. The shape is the result of melting and rapid recrystaUi2ation during... 

The production of the polymer depends on several factors such as the composition of the growth medium, the time of harvest, and the particular stage of the life-cycle of organism under consideration. Eor P. polycephalum only plasmodia are the producers of j8-poly(L-malate) neither amoebae nor spherules (specialized cell forms that can survive unfavorable environmental conditions)... 

Hematite in the soil is concentrated in spherules and their fragments, which are abundant on nearly all soil surfaces. Several trenches excavated using the rover wheels showed that the subsurface is dominated by basaltic sand, with a much lower abundance of spherules than at the surface. Olivine-bearing basaltic soil is present throughout the region. At several locations along the rover s traverse, sulfate-rich bedrock outcrops are covered by no more than a meter or so of soil. 

Fig. 8.36 Leyt Spectrum of the soil close to the crater rim where Opportunity entered and exited the crater. The basaltic soil is unusually high in hematite (but no indication of significant contribution Irom hematitic spherules). Middle rover tracks. Right 750 m diameter (. 75 m deep) eroded impact crater Victoria Crater, formed in sulfate-rich sedimentary rocks. Image acquired by the Mars Reconnaissance Orbiter High-Resolution Science Experiment camera (Hirise). The red line is the drive path of Opportunity exploring the crater. (Courtesy NASA, JPL, ASU, Cornell University)...

Fig. 8.37 Left, spectrum of an accumulation of hematite rich spherules (Blueberries) on top of basaltic soil (Sol 223-228 of the mission 1 Sol = 1 Martian day). The spectrum is dominated by the hematite signal. Estimations based on area ratios (bluebeiries/soil) and APXS data indicate that the blueberries as composed mainly of hematite. Right MI picture (3x3 cm ) of hematitic spherules (blueberries) on basaltic soil at Meridiani Planum...

The soil close to the crater rim, at the exit point of Opportunity, shows a high hematite content in the Mossbauer spectrum (Fig. 8.36), which can be attributed to the presence of hematite spherules blueberries). 

Undifferentiated meteorites these are derived from asteroids which never underwent the heating which leads to fusion. They consist of millimetre-sized spherules (chondrules) embedded in a matrix. 

Each GaSb whisker is grown from a ball-shaped center and is capped by a spherule containing amorphous Ga as was shown by SAED (no... 

Micelles are capable of self-replication if an appropriate chemical reaction occurs within the micelle itself that produces more of the same amphiphile that forms the micelle. Such self-replication has been demonstrated for both ordinary micelles in an aqueous medium [139] as well as for reverse micelles, [140] which are spherules of water stabilized by an amphiphile in an organic solvent. Some of the prebiotic potentialities of replicating membranous vesicles have been investigated, [141] and they have been characterized as "minimum protocells. [142]... 

Vaporization processes that produce the high 5 Fe values of deep sea spherules are, of course, more complicated, because a large portion of the heating and vaporization occurs in the atmosphere, and is accompanied hy conversion of Fe metal to Fe oxides. 

Herzog GF, Xue S, Hall GS, Nyquist LE, Shih C-Y, Wiesmann H, Brownlee DE (1999) Isotopic and elemental composition of iron, nickel, and chromium, in t>pe I deep-sea spherules Implications for origin and composition of the parent micrometeoroids. Geochim Cosmochim Acta 63 1443-1457 Holland HD (1994) Early Proterozoic adnospheric change. In Early Life on Eardi, Noble Symposium No 84. 

The micrometeorites that melt during passage through Earth s atmosphere tend to solidify as spheres. These are termed cosmic spherules. The mineralogy of these spherules is given in Table 13.2. Their high iron and nickel content make them much denser (3 to 6g/cm ) than continental rock ( 2.7g/cm ). Like aeolian particles, cosmic dust deposited on the sea surface eventually settles to the seafloor via pelagic sedimentation. 

We saw in Section 13.6 that hydrolysis and subsequent polymerization of aqueous metal cations can lead to the precipitation of gels. In the case of Fe(H20)63+ in mildly acidic solutions, the polymerization sequence of Eqs. 13.25 and 13.26 and Fig. 13.6 first reversibly forms cationic colloidal spherules, 2-4 nm in diameter, with the structure of 7-Fe0(0H) [double chains of Fe(0,0H)6 octahedra] on a timescale of about 100 s. These lose H+ and harden over several hours and then, over several days, form aged polymer rods, then rafts, and ultimately, after several months, needles of solid goethite [cc—FeO(OH)].1,2 Thus, aging is an important feature of hydrolytic polymerization. 

This resin is soluble in the cold in alcohol, ether, benzol, turpentine, bisulphide of carbon, and ebloro form all these liquids, when evaporated, leave as residue the amorphous resin. Dilute acids, concentrated alkaline solutions, and ammonia, do not attack the yellow resin. Monohydra tod sulphuric and nitric acids act upon it rapidly, producing phenomena analogous to those exhibited with the other two principles. Hydrochloric acid, even in ite sate rated solution at 68°, a without action upon it. But the most remarkable character of this resin Is the power of forming, under the circumstances already indicator , those globose crystals covered with a white pellicle of anothor resin, and presenting In their complex form the appearance of opaline spherules. 

Formates. — The simplest Tnowo-carboxylic acid is formic acid (HCOOH). Formate complexes have not been extensively investigated although Sakkar [353] has mentioned rare earth formates. The cerium group rare earths form spherulic formates which are hexagonal. This property is used to identify small amounts of these elements. These formates are prepared by dissolving freshly prepared rare earth hydroxides in formic acid. 

Tiny transliicem-io-opaque glassy spherules are prominent in ihe lunar rcgoluh, wtlhm which ilnienite (as thin plates) with minor olivine are present. 

PERLITE (or Pearlstone). An unusual form of siliceous lava composed of small spherules of about the size of bird shot or peas. It is grayish in color with a soft pearly luster. The spherules often show a concentric structure and are believed to be funned as a result of a peculiar spherical cracking developed while cooling. They may be confused with oolites, which are classified as concretions. 

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