Are geodes metamorphic, igneous, or sedimentary rocks?
Caroline That’s a good question! Let’s first look at a definition of what a geode is: A hollow rounded rock nodule filled with an inner lining of mineral matter. Sand, water, or petroleum may fill the cavity, or the lining may consist of crystallized calcite, quartz, or other minerals. We should also consider the definitions of the 3 types of rock: Igneous – rock formed from a melt. Sedimentary – rock formed from the deposition of particles of minerals in layers or beds. Metamorphic – rock formed by the effects of added heat or pressure to another rock. Not one of these definitions really fits because these definitions define processes! What we find is that with some types of stones it is that the forms that they take (like geodes, concretions, nodules, and many others) that we as geologist use to describe them. So a geode is an aggregate of minerals that do not quite fit the definitions we geologists so neatly give concerning the 3 rock types. This is because the terms we use, like ge
