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Geodes (Greek γεώδης - ge-ōdēs, "earthlike") are geological secondary structures which occur in certain sedimentary and volcanic rocks. They are themselves of sedimentary origin formed by chemical precipitation. Geodes are essentially hollow, loosely spheroid to oblate masses of mineral matter that may have formed.

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Greenstone -- (Michigan's state gem) was formed in gas bubbles within basalt. Basalt is a volcanic rock, formed in Michigan in part during the Midcontinent Rift approximately one billion years ago. It is found more in the western Upper Peninsula, MI, USA

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from The Telegraph

Environment

The Church of St. George or Bet Giyorgis in Lalibela, Ethiopia. Its roof is cut into the shape of a square cross, and visitors enter the church via stairs cut down into the volcanic rock. These stairways deepen into trenches that connect to a tunnel that opens to the base of the church and its entrance. Monolithic churches were carved out of the ground to which they are still attached. Eight hundred years ago the Ethiopian King Lalibela had a divine vision to carve a new Jerusalem from…

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De l'art gratuit dans la nature. La lave d'un volcan crée des structures et des plis comme des drapés qui peuvent stimuler l'inspiration. // Free and natural art found in nature. Lava from a volcano creates structures and drape-like folds that can be quite inspiring.

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