cumulate

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cumulate Applied to igneous intrusive rocks formed by the accumulation of crystals as a result of gravity settling. It is typical of layered intrusions and common in some differentiated meteorites. The early-formed minerals are called ‘cumulus’ minerals and show a regular variation in composition with their height in the intrusion. See MINERAL LAYERING.

cumulate

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cumulate XVI. f. pp. stem of L. cumulāre, f. cumulus heap; see -ATE 3.
So cumulative XVII. cumulus heap, accumulation XVII; (meteor.) cloud of rounded masses heaped one on the other XIX.