Tag Archives: silica-rich fluids

Geo-pic of the week: Mineralized Vug in Chert

mineralized vug in chert

Pictured above is a mineralized vug (approximately 3 inches long) in chert.  A vug is a void or open space in a rock.  Many vugs are filled with minerals after water that is saturated with a certain mineral flows through the rock. This mineralization can happen in multiple stages. The vug above was initially filled with silica-rich fluid therefore quartz precipitated out of solution and lined the walls of the vug.   Afterwards calcite precipitated, as is evident from the larger crystal on the interior left of the vug. 

This vug is present in a section of ornamentally banded chert.  Chert is a sedimentary rock made up of microcrystalline quartz.  It can be a variety of colors or banded and quite beautiful.  The chert above is Devonian age (416-359 million years ago) from northwest Arkansas.

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GeoPic of the Week: Large Quartz Vug

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This large quartz vug, or cavity, (approximately 3 ft wide x 3 ft high) was extracted from one of the Coleman Quartz Mines and brought to the Arkansas Geological Survey Learning Center in the 1980s. This vug was found in the Crystal Mountain Sandstone (Early Ordovician, 485-470 mya), a massive, coarse-grained, well rounded, light gray sandstone from Montgomery and western Garland Counties, Ouachita Mountains. These quartz crystals formed secondarily from silica-rich fluids that resided within this large cavity.