Abstract

A previously unreported, coarsely crystalline calcite fills pores and is composed of crystals that possess inclusion-patterns and lattice-curvatures mimetic after bundled acicular carbonate cements. This calcite fabric, named 'fascicular-optic' because of the characteristic divergent optic-axis pattern within each crystal, is possibly widely distributed in certain limestones. It has been found within both shallow-marine and deep-water (pelagic) limestones. The replacement mechanism responsible for generating fascicular-optic calcite is believed to involve the lateral joining together (coalescence) of the former acicular crystals, either directly if the original cement had a low-Mg calcite mineralogy, or by coalescence of acicular aragonite or high Mg-calcite crystals, followed by subsequent stabilization (calcitization or magnesium loss).

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