Figure 7-5. Tops of three layers of calcite (C) below a layer of aragonite (A). Layer in middle has calcite crystals with euhedral terminations (large red arrows), whereas upper layer has less well developed terminations (green arrow) and lower layer is flat (blue arrows) with no visible crystal terminations. Euhedral crystal terminations of middle layer are evident because a zone of very small calcite scalenohedra (small red arrows) formed on top of them. This is an unusual microfabric, in that the boundary between one calcite layer and an overlying calcite layer is usual subtle, because the overlying calcite nucleates on the lattice of the underlying layer, and no new crystals form. In this case, many small crystals (at small red arrows) nucleated atop the euhedral layer.
     Photomicrograph was taken in plane-polarized light; field of view is 1.7 mm wide. Carlsbad Caverns, New Mexico, southwestern U.S.A.; Georgia Giant Stalagmite; thin section CB63. Sample collected by Dr. George A. Brook.
  Speleothem Image
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