Classification of Sedimentary Rocks

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Sedimentary rocks are classified according to two(2) major classes known as: •Clastic (detrital) Sedimentary Rocks
Chemical Sedimentary Rocks

Clastic (detrital) Sedimentary Rocks
1.Made up of mineral grains, fragments of other rocks (called lithic fragment), shells and other inorganic(hard) of formally living organisms. 2.The clastic particles or grains in a sedimentary rocks are cemented together by mineral precipitates that formed during the process of diagenesis. 3.These rocks are divided according to sizes of component particle such as: a)Rudaceous Deposits

b)Arenaceous Deposits
c)Argillaceous Deposits

a) Rudaceous Deposits (Latin word for gravelly)
Boulders, cobbles, pebbles and granules are generally pieces of rock e.g. flint and granite which are greater than 2 mm. •Marine rudaceous deposits are formed at the foot of cliffs from the break up or falls of rock and materials drifting across the coastline and some are deposited in the fluvial environment. •Examples of rocks are conglomerate (rounded clasts) and breccia (angular clasts).


b) Arenaceous Deposits (Latin word for sandy)
Most sand-grains are composed of quartz and they may be rounded, sub-angular or angular according to the degree of transport and attrition to which they have been subjected. •Other minerals that occur in sands are feldspar, mica, apatite, garnet, zircon, tourmaline and magnetite, usually present in a small amount. •The porosity of these deposits depends on several factors: 1. The grade sizes of grains.

2. The amount and kind of packing which the grains
have acquired.
3. The amount of cement present.
Examples of rocks are many types of sandstone.


c) Argillaceous Deposits (French word for silty)
Clays and silts are muddy sediments (< 0.002 mm) deposited slowly in still water on the continental shelf or in lakes and...
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