![]() Nodules are formed in many different ways, usually from sediments weathered and exposed to various chemicals in groundwater over time. It is amazing to think how pressure, temperature, evaporation and long periods of time create geodes. Geodes that form in volcanic rock gas cavities are called amygdules, which contain bands of chalcedony and quartz, as well as calcite crystals. Some geodes even form alongside bituminous coal. Some of these minerals, depending on their location, may have originated from ancient fossils of sea animals like diatoms and sponges. Then, when water manages to get into this cavity, it carries any dissolved minerals along with it, and these can form crystals that grow toward the center of the geode. ![]() For limestone geodes, a cavity forms from either geological or biological processes. Thin slabs of stone with irregular shapes. for stonework include those made of flat. For volcanic ash bubbles, water passes into them over long periods of time, and these eventually solidify. and translucent variety of gypsum, generally white in color. They can arise in volcanic rock bubbles, in sediment bubbles or in hollows of limestone. Marble is a soft rock and, unlike quartzite which can look slightly similar, white marble will not scratch glass. Pure white marble has a medium grain texture and is smooth to the touch with easy-to-see crystals. ![]() ![]() Geodes can form through various methods involving chemical and physical processes. In its pure white form, marble is composed of calcium carbonate and may contain other minerals, including graphite, quartz, and pyrite. ![]()
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