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Sediments and Sedimentary Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Fossils may be intact and up to centimeters in size, but many are only fragments of once larger fossils, and many are very fine grained. The size depends on the organism that created the fossils and how much the fossils were broken before lithification. Ooids are spheres of calcite that have a concentric, snowball-like structure created when carbonate layers grow around a small seed particle. Ooids generally form when particles roll around in shallow water, adding additional material to their outsides in the same way that children make large snowballs by rolling them. Figure 8.68 shows two views of ooids. The top is a standard photo, and the bottom is a photo of a thin section (a very thin slice of rock) taken with a microscope.
Sedimentary rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Ooids These are spherical or ellipsoidal grains up to 2 mm in diameter which have regular concentric laminae of fine-grained carbonate developed around a nucleus. They form by precipitation from supersaturated solution while held in suspension in turbulent waters.
Effective poroelastic properties of N-layered composite sphere assemblage: An application to oolitic limestone
Published in European Journal of Environmental and Civil Engineering, 2023
H.T. Trieu, N.B. Nguyen, M.N. Vu, T.T.N. Nguyen, N.H. Tran, D.T. Pham, T. Nguyen-Sy
The considered material is an oolitic limestone from Bourgogne (France). Its microstructure and poroelastic properties were experimentally investigated by Lion (2004), Lion, Ledésert, et al. (2004), and Lion, Skoczylas, et al. (2004). Different observation techniques including X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS) were used for petrographic study. The studied rock is monomineralic that its main component is calcite. Microstructure characterisation evidenced that the Bourgogne limestone is essentially an assemblage of ooids with size 100–1000µm made of concentric spheres of calcite made of concentric calcite spheres (Figure 2). Ooids are surrounded by the cement matrix where both sparite (coarse crystalline calcite) and minor micrite (micro-crystalline calcite with a grain size finer than 4µm) are present (see Figure 2–right). SEM photomicrograph shows that an ooid is constituted by micrite crystals and microporosity (Figure 3).