free download PNG images :Chalk

Chalk is a soft, white, porous sedimentary carbonate rock, which is a limestone form composed of calcite minerals. Calcite is an ionic salt called calcium carbonate or CaCO3. It is formed by gradually accumulating small calcite shells (coconut shells) (known as Spheroides) under certain depth of ocean conditions. Flint (a kind of stone peculiar to chalk) is very common. It is a strip parallel to the bed or a summary embedded in chalk. When water is discharged upward during compaction, it can come from spongy needles or other siliceous organisms. Flint is usually deposited around larger fossils, such as the fossil (Echinoidea), which may be silicified (i.e. replaced by flint molecule by molecule).

Cretaceous seen in Cretaceous sediments of Western Europe is not common in thick sedimentary limestone. Unlike most of the thicker limestone sequences (such as Carboniferous limestone or Jurassic Oolitic Limestone), most of the Cretaceous cliffs have almost no obvious bedding. Presumably, this shows that for tens of millions of years, the situation has been very stable.

The "nijana chalk curve" in the west of Negev, Israel, is a Cretaceous sediment formed in the Mesozoic Tethys ocean

Chalk is more resistant to weathering and collapse than the clay that usually accompanies it, thus forming steep cliffs where the chalk ridge contacts the sea. Chalk hill, commonly known as chalk hill, is usually formed where the chalk belt reaches the ground at an angle, thus forming a steep slope. Because the chalk is well connected, it can hold a large amount of groundwater and provide a natural reservoir, which can release water slowly in the dry season.