HRTEM of microcrystalline opal in chert and porcelanite from the Monterey Formation, California

@article{Cady1996HRTEMOM,
  title={HRTEM of microcrystalline opal in chert and porcelanite from the Monterey Formation, California},
  author={Sherry L. Cady and H. R. Wenk and Kenneth H. Downing},
  journal={American Mineralogist},
  year={1996},
  volume={81},
  pages={1380 - 1395}
}
Abstract Microcrystalline opal was investigated using low-dose transmission electron microscopy (TEM) methods to identify microstructural characteristics and possible phase-transformation mechanisms that accommodate silica diagenesis. High-resolution TEM (HRTEM) revealed that microcrystalline opal in opal-CT chert (>90 wt% silica) and opal-CT porcelanite (50-90 wt% silica) from the Miocene Monterey Formation of California displays various amounts of structural disorder and coherent and… 

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References

SHOWING 1-10 OF 102 REFERENCES
Structural defects in microcrystalline silica
The structure of the microcrystalline silica varieties chalcedony, flint, moganite, opal-C and -CT is characterized by X-ray powder diffractometry and transmission electron microscopy (TEM). The role
Transmission electron microscopy of coexisting low-tridymite polymorphs
Abstract Three polymorphs of tridymite (MC, PO-10 and MX) have been examined by transmission electron microscopy (TEM), in crystals which also contain lamellae of cristobalite. MX is the least
Diagenetic trends in the siliceous facies of the Monterey Shale in the Santa Maria region, California
X-ray diffraction and oxygen isotopic analyses of outcrop and subsurface samples of siliceous rocks were used to reconstruct thermal and diagenetic histories of the Miocene Monterey Shale near Santa
Intergrowth and twinning in opal-CT lepispheres
Under conditions of unobstructed diagenetic growth, opal-CT usually forms spherical aggregates, so-called “lepispheres”. From a scanning electron microscope study of deep-sea porcelanites, the
Origin and distribution of silica lepispheres in porcelanite from the Monterey Formation of California
ABSTRACT Samples of porcelanite from the Monterey Formation (Miocene) of California were examined by scanning electron microscopy and were found to contain numerous small cavities partially filled
Progressive ordering of cristobalitic silica in the early stage of diagenesis
Examination of hydrothermally transformed silica from controlled experiments reveals that amorphous silica changes to quartz through an intermediate phase of opal-CT and that the d(101) spacing of
Silica diagenesis; II, General mechanisms
ABSTRACT Amorphous silica phases (opal-A) precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions.
Characterization of synthetic tridymites by transmission electron microscopy
Eight tridymites, synthesized in a variety of ways, have been examined by transmission electron microscopy (TEM). Each sample appeared to be heterogeneous, containing a mixture of low temperature
The nature of water in chalcedony and opal-C from brazilian agate geodes
The water species (H2O(SiOH) and H2O(mol)) of length-fast chalcedony and opal-C in Brazilian agates were studied with thermoanalytical, chemical and infrared absorption methods. Specific surfaces
...
...