Amygdaloidal basalt

Decorative conglomerates are sometimes referred to as puddingstones. This term is also sometimes used for amygdaloidal basalt or any other specimen that contains rounded clasts or nodules of a contrasting color to the matrix. 

Note HAB = highly amygdaloidal basalt MAB = amygdaloidal basalt. 

The thickness of the flows ranges from less than 1 m to more than 120 m. All flows have amygdaloidal zones at their bases and tops and the vesicles are filled with zeolites, quartz, and calcite. The thickest flows are coarse grained and have diabasic texture. Tobin Mesa is capped by a black flow composed of aphanatic to glassy basalt. 

Most of the flows are amygdaloidal, some have diabasic texture, and one flow contains pillow-like bodies (i.e pahoehoe toes). In addition, two flows contain petrified three trunks and a sedimentary interbed near the top of the section. Elliot (1970a) also published a stratigraphic section of the basalt flows on Mt. Bumstead in the Grosvenor Mountains near the Otway Massif. 

The Plogen nunatak consists of about 30 basalt flows most of which are porphyritic with phenocrysts of plagioclase, ohvine, and pyroxene in a groundmass of plagioclase laths, clinopyroxene, Fe-Ti oxides, and mesostasis. The plagioclase phenocrysts of many flows are altered to sericite and, in some cases, have been converted to pseudomorphs of saussurite (mixture of alteration products containing chlorite, calcite, albite, and epidote). Olivine was also altered, but clinopyroxene is pristine, hi contrast to the pervasive alteration of the flows, the basalt dikes are unaltered. The flow tops are typically amygdaloidal and the former vesicles are filled with chlorite, quartz, prehnite, and calcite. 

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