GeoJeopardy! Fridays #72

Time for GeoJeopardy! Fridays, because it's a lazy day so far.

- Rock -

More than half of sedimentary rock is this type from which oil & natural gas can be obtained

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  Trachyte & rhyolite are the most common varieties of this porous igneous volcanic rock

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 On average rocks consist of 46.5% this gaseous element

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 In its purest form, this rock used in the cement industry contains only calcite

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Chert, a hard, dense sedimentary rock, is called jasper if it's brightly colored, & this if it's dark

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All the answers as well as any other previous GeoJeopardy! questions can be found over at my website by clicking the link.

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Questions, images, and videos courtesy of j-archive.com