Unformatted text preview: silica-secreting organisms such as diatoms, radiolarians, or some types of sponges. Chert is formed through chemical reactions of silica in solution replacing limestones. Chert: Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or micro fibrous sedimentary rock that may contain small fossils. It varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty red Flint: Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of Chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones Jasper: Jasper, a form of chalcedony , is an opaque, impure variety of silica, usually red, yellow, brown or green in color. Blue is rare. This mineral breaks with a smooth surface, and is used for ornamentation
Jasper 12 Geology & Geophysics in Oil Exploration Mahmoud Sroor Chert Flint Geology & Geophysics in Oil Exploration 7-Volcanic Sediments Some volcanic particles are generated by weathering and erosion (epiclastic) and therefore differ only in composition from nonvolcanic clasts. Other volcanic particles are formed instantly by explosive processes and are propelled at high velocities (>100 m/s) along the surface of the earth or high into the atmosphere (>40 km above the earth). • Pyroclastic Deposits: It refers only to volcanic materials ejected from a volcanic vent, Volcanologists also refer to airborne fragments as pyroclasts • Pumice is a highly vesicular glass foam, generally of evolved and more rarely of basaltic composition with a density of <1 gm/cm3 & may have porosity >50% • Scoria (also called cinders), usually mafic (Basic magma), are particles less inflated than pumice. They readily sink in water. They are generally composed of tachylite, that is, glass rendered nearly opaque by microcrystalline iron/titanium oxides. • Tephra: is fragmental material produced by a volcanic eruption regardless of composition, Tephra fragments are classified by size:
• • • • Scoria Pumice • • • Ash: particles smaller than 2 mm (0.08 inches) in diameter Lapilli or volcanic cinders: between 2 and 64 mm in diameter Vo...
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- Spring '10
- Geology, Volcano, Tephra, Volcanic Ash, Geology & Geophysics, Mahmoud Ahmed Sroor