New answers tagged mineralogy
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You almost got the answer yourself. The rock is definitely lignite. As a confirmatory test, you could scorch it with a blow lamp or put it on a fire. If it's lignite it will burn.
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These globular structures are called varioles, and there is not complete agreement as to how they are formed. The most likely theory is that the basalt has been hydrothermically altered by millions of years of water infiltration bringing in tiny amounts of other minerals, but the jury is still out.
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