shells dissolved forming a silica rich gel chert then formed when the gel

Shells dissolved forming a silica rich gel chert then

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shells dissolved, forming a silica-rich gel ; chert then formed when the gel solidified - Flint, jasper, agate, and petrified wood are all forms of Chert. Cherts (replacement) : - discovered by a tribe of Native Americans (the Onondaga)
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- limestone contain layers or nodules of black chert, this type of chert formed when cryptocrystalline quartz gradually replaced calcite crystals within a body of limestone long after the limestone was deposited; that’s why it’s called ‘replacement chert’ - Chert comes in many colors (black, white, red, brown, green, gray) depending on the impurities it contains two types of Chert mentioned in the book: - Petrified wood : chert that forms when silica-rich sediment, such as ash from a volcanic eruption, buries a forest, the silica dissolves in a groundwater, and then later precipitates as cryptocrystalline quartz within wood, gradually replacing the wood’s cellulose -> the chert deposits retains the shape of the wood and the growth rings within it - Agate : precipitates in concentric rings inside hollows in a rock and ends up with a striped appearance, caused by variations in the content of impurities incorporated in the chert 12. Style of Volcanic Edifices : Shield Volcano - made from successive flows of low-viscosity basalt, has very gentle slopes - low profile, the shape is due to the series of thin and fluid lava flows (low in Si concentration) that slowly spread and give the volcano a shield like shape, (wider and shorter) - ex: Hawaiian volcanoes Cinder Cone - the pile of cinders has assumed the angle of repose, a lava flow covers the land surface in the distance (viscous lava ~ high in Si) Stratovolcano (Composite Volcanoes) - Layers of tephra and lava, volcanic debris flows and ash avalanches modify slopes and contribute to the development of a classic cone-like shape - Magma from this type of volcano is high viscosity and Silica rich
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