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  2. Geode - Wikipedia

    en.wikipedia.org/wiki/Geode

    After rock around the cavity hardens, dissolved silicates and/or carbonates are deposited on the inside surface. Over time, this slow feed of mineral constituents from groundwater or hydrothermal solutions allows crystals to form inside the hollow chamber. Bedrock containing geodes eventually weathers and decomposes, leaving them present at the ...

  3. Concretion - Wikipedia

    en.wikipedia.org/wiki/Concretion

    Groundwater containing methane or petroleum from underlying rock beds reacted with the iron oxide, converting it to soluble reduced iron. When the iron-bearing groundwater came into contact with more oxygen-rich groundwater, the reduced iron was converted back to insoluble iron oxide, which formed the concretions.

  4. Cementation (geology) - Wikipedia

    en.wikipedia.org/wiki/Cementation_(geology)

    Calcite cement in an ooid-rich limestone; Carmel Formation, Jurassic of Utah. Minerals bond grains of sediment together by growing around them. This process is called cementation and is a part of the rock cycle. Cementation involves ions carried in groundwater chemically precipitating to form new crystalline material between sedimentary grains ...

  5. Vein (geology) - Wikipedia

    en.wikipedia.org/wiki/Vein_(geology)

    White veins in dark rock at Imperia, Italy. In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation. [1]

  6. Dakota Formation - Wikipedia

    en.wikipedia.org/wiki/Dakota_Formation

    Ground water flowing from inland reacted with changes in pH, oxygenation, and salinity as it encountered seawater, depositing iron oxide and calcite in underground layers near shorelines. These minerals hardened the material and fossils to preserve evidence of the ecology of those environments. [ 5 ]

  7. Enhydro agate - Wikipedia

    en.wikipedia.org/wiki/Enhydro_agate

    This is a three phase inclusion in rock crystal quartz. The solid is a black material that is of bituminous origin. The liquid encased is petroleum, and the gas bubble is methane. Enhydros are formed when water rich in silica percolates through volcanic rock, forming layers of deposited mineral. As layers build up, the mineral forms a cavity in ...

  8. Geology of the Death Valley area - Wikipedia

    en.wikipedia.org/wiki/Geology_of_the_Death...

    Little is known about the history of the oldest exposed rocks in the area due to extensive metamorphism.This somber, gray, almost featureless crystalline complex is composed of originally sedimentary and igneous rocks with large quantities of quartz and feldspar mixed in. [1] The original rocks were transformed to contorted schist and gneiss, making their original parentage almost unrecognizable.

  9. Silicification - Wikipedia

    en.wikipedia.org/wiki/Silicification

    Silicification happens when rocks or organic materials are in contact with silica-rich surface water, buried under sediments and susceptible to groundwater flow, or buried under volcanic ashes. Silicification is often associated with hydrothermal processes. [1]

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