Amygdaloid

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amygdaloid

[ə′mig·də‚lȯid]
(geology)
Lava rock containing amygdules. Also known as amygdaloidal lava.

Amygdaloid

 

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.

References in periodicals archive ?
Hematite is found in amygdaloidal cavities as druses of silvery black microscopic crystals on datolite, prehnite, albite, calcite, heulandite and stilbite.
The volcanics are amygdaloidal in nature and exhibit porphyritic, cumulophyric and intergranular textures.
Some mineralization also occurs in the basalt above this horizon, in veins that transect the flows and in vertically bulging, dome-like regions of amygdaloidal basalt, referred to as diapirs by Laskowich and Puffer (1990).
While the overlying aa makes excellent building stone, the pahoehoe beneath it is unsuitable for building because it is too soft, amygdaloidal, and full of mineralized vesicles.
Massive amygdaloidal and porphyritic basalts occur in the northeastern and central regions of the study area.
The amethyst crystals occur in small to large clefts, or cleft-systems, which are similar to Alpine clefts and fundamentally different from geodes or amygdaloidal cavities which are the result of gas bubbles in lava.
The UFU, of minimum 100 m thickness, is again dominated by massive, columnar-jointed, medium-grained basalt containing <20-30% mesostasis, and with minor amygdaloidal zones containing zeolite minerals.
Most basalt in the area is massive, but considerable amounts are amygdaloidal. Zeolites at Wasson Bluff commonly occur in basalt, conglomerate with basalt clasts, and less commonly in sandstone, but on average make up no more than 3% of the overall rock.
The upper 5 to 8 meters of this first flow is amygdaloidal and contains the majority of the best specimen-quality minerals.
The Eastport Formation in New Brunswick comprises amygdaloidal mafic flows and agglomerate, massive to flow-banded felsic flows, welded and non-welded lapilli tuff, pisolitic tuff, peperitic breccia, and grey to maroon sandstone and conglomerate totalling ~4000 m (Hay 1967; Pickerill and Pajari 1976; Pickerill et al.