Oco Geode Dimensions:  2.8" x 1.4" x 1.5" Weight:  154 grams (5.4 oz) Color:  Black/Gray/White (Natural) This Oco geode from Brazil has a cut and polished face.  You'll receive the exact Oco shown in the pictures. An Oco is a small geode with a thin agate shell and a hollow interior lined with quartz crystals.  Ocos form in hollow cavities in volcanic or sedimentary rocks, most commonly basaltic lavas and limestones.  The cavities themselves may have been gas bubbles in magma, or may have formed when nodules inside sedimentary rocks dissolved.  As mineral-laden groundwater or hydrothermal fluid seeps through the hollow cavities, chemical precipitation begins to fill the hollows from the outside in. Please visit my store, Mother Lode Rock Shop, for more Ocos and other Rocks, Minerals, and Fossils.  Thank you for looking.