Makeup of New Jersey's Palisades (6)

I believe the answer is:

basalt

(Other definitions for basalt that I've seen before include "Dark fine-grained volcanic rock" , "Commonest type of solidified lava; dense, dark grey and fine-grained" , "rock from 2 [VOLCANO]" , "Dark rock of volcanic origin" , "Type of rock is a blast, oddly" .)

I've seen this clue in The Wall Street Journal.

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