Types of Non - Clastic (Chemical)Sedimentary Rocks

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Types of Chemical (Non-Clastic) Sedimentary Rocks

Chemical or non-clastic sedimentary rocks form from the precipitation of minerals from solution due to evaporation, chemical reactions, or biological activity. They are classified based on their mineral composition and formation process.

1. Limestone
Composition: Calcium carbonate (CaCO₃), mainly in the form of calcite or aragonite.
Formation Process: Precipitation of calcite from seawater or accumulation of marine organism shells.
Depositional Environment: Shallow marine, coral reefs, caves, and lakes.

Varieties:
Fossiliferous Limestone – Contains visible fossils.
Chalk – Made of microscopic marine organisms (coccolithophores).
Travertine – Forms in caves and hot springs.

2. Dolostone (Dolomite Rock)
Composition: Dolomite (CaMg(CO₃)₂).
Formation Process: Forms when magnesium-rich water alters limestone.
Depositional Environment: Shallow marine and lagoonal settings.

Key Feature: Harder and less reactive to acid than limestone.

3. Chert
Composition: Microcrystalline silica (SiO₂).
Formation Process: Silica precipitates from water or replaces limestone.
Depositional Environment: Deep marine, groundwater deposits.

Varieties:
Flint – Dark-colored, used for tools.
Jasper – Red due to iron impurities.
Agate – Banded chert found in volcanic regions.

4. Evaporites
Form due to evaporation of mineral-rich water in arid environments.

Key Features:
Halite has a salty taste and cubic crystals.
Gypsum is softer and can be scratched with a fingernail.

5. Iron-Rich Sedimentary Rocks
Composition: Iron oxides (hematite, magnetite) and iron carbonates.
Formation Process: Precipitation of iron from seawater.
Depositional Environment: Ancient ocean basins (Banded Iron Formations, or BIFs).

Key Feature: Important source of iron ore.


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