BASALT![]() A basic volcanic rock consisting of calcicplagioclase feldspar and pyroxene, basalt is the most abundant of all lava types. Apatite and magnetite are nearly always present, while olivine may also occur. It forms by the cooling of highly mobile basaltic lavas. Because of their fluidity, they may form very thick lava sheets. Basalt occurs widely in continental areas, and is the principal rock of the ocean floor. One of the best studied active basaltic volcanoes, Mauna Loa, forms much of the island of Hawaii.
![]() Amygdaloidal Basalt
Amygdaloida basalt is a basic volcanic rock with a total silica content of 45 to 55 per cent. Calcium-rich plagioclase feldspar and pyroxene are the main minerals. Olivine and magnetite are other minerals that are frequently associated with amygdaloidal basalt. Numerous amygdales (small, rounded gas-bubble cavitites infilled with minerals) are characteristic of some basalts, Zeolites and quartz - often in the form of agate - are common minerals.
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