Amygdaloid(redirected from amygdaloids)
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an effusive rock with large, slightly elongated pores filled with secondary deposits of various minerals (quartz, zeolites, chlorites, and calcite). The term “amygdaloid” refers to the texture of the effusive rock regardless of its mineral composition. There are diabase, basaltic, porphyritic, and other types of amygdaloids. Amygdaloids are particularly common among ancient volcanic strata that have been subjected to hydrothermal alteration in the zeolitic facies of metamorphism.