Some sponges also produce “spicule” of silica. In some parts of the ocean and in shallow seas, manyĭiatoms and radios live in the water. Part of the silicon dioxide in the container is thought to it formed in this way is a chemical sedimentary rock. If the nodules or concretes are numerous, they can grow enough to be joined together to form a nearly continuous notch layer in the sedimentary mass. Into irregularly shaped nodules or concretes. Of groundwater, a large number of silicon dioxide microcrystals are transformed When the dissolved silica is transported to the formation zone by the movement In soft sediments that will become limestone or chalk. Chert FormationĬhert may occur as the microcrystals of silicon dioxide grow Bedded variety seems to be often associated with turbidity currents. So It is also sometimes said to be a rock of chemogenic origin. It may move as a silica-rich liquid and form nodules in rocks by replacing the original (usually carbonate) material. Although the material it is made of ultimately came from siliceous tests of marine species, the rock itself is often not deposited in situ. Their siliceous tests are not made of quartz initially, but after burial, compaction, and diagenesis, opaline siliceous sediments transform to quartz. Sometimes microscopic fossilized remains of these sea creatures may be preserved in these rocks. Chert CompositionĬhert is in most cases a biogenic rock, it is made of siliceous tests of diatoms, radiolarians, siliceous sponge spicules, etc. Include firestone, silex, silica stone, chat, and flintstone. Other lesser used terms for chert (most of them archaic) Siliceous sinter is porous, low-density, light-colored siliceous rock deposited by waters of hotĭistinction because of its unique variation of colors and its ability to take a Term used for fine-grained siliceous rocks with a texture and a fracture Magadi-type chert is a variety that forms from a sodium silicate precursor in highly alkaline Without petrological training confuse opal with chert due to similar visible Microcrystalline and contain much less water (sometime none). Mineral (it is a mineraloid) and it is generally not considered a variety ofĬhert, although some varieties of opal (opal-C and opal-CT) are Onyx is a banded agate with layers in parallel lines, often black and white. Radiolarite is a variety of this rock formed as primary deposits and containing radiolarian microfossils.ĭistinctly banded chalcedony with successive layers differing in color or Jasper frequently also occurs in black, yellow or even green (depending on the type of iron it contains). Jasper is a variety of this rock formed as primary deposits, found in or in connection with magmatic formations which owes its red color to iron(III) inclusions. Known Common chert is a variety of chert which forms in limestone formations by replacement ofĬalcium carbonate with silica. Marly limestone formations formed by a replacement of calcium carbonate with silica. It was originally the name for chert found in chalk or There are many varieties of chert, that classified visible, Beds of marine diatomaceous chert comprising strata several hundred meters thick have been reported from sedimentary sequences. Diatomaceous chert consists of beds and lenses of diatomite which were converted during diagenesis into dense, hard chert. It also occurs in diatomaceous deposits and is known as diatomaceous chert. The banded iron formations of Precambrian age are composed of alternating layers of chert and iron oxides. Thick beds of chert occur in deep marine deposits. It also occurs in thin beds, when it is a primary deposit (such as with many jaspers and radiolarites). if where it occurs in chalk or marl, it is called flint. Occurrence of ChertĬhert occurs in carbonate rocks that are greensand, limestone, chalk, and dolostone formations as exchange mineral, where it is formed as a result of some type of diagenesis. To touch, glassy, exhibits conchoidal fracture. Name origin: Term is used to refer generally to all rocks composed primarily of microcrystalline, cryptocrystalline and microfibrous quartzĬannot be seen except under very high magnification.Ĭolours, dependent on impurities present when precipitated. It occurs as nodules, concretionary masses, and as layered deposits. It is usually organic rock but also occur inorganically as a chemical precipitate or a diagenetic replacement. Chert is a fine-grained sedimentary rock composed of quartz (SiO2) that is microcrystalline or cryptocrystalline quartz.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |