A chalk coastline is a type of coastline that is characterized by cliffs and other features made primarily of chalk. Chalk is a soft, white, porous rock formed from the accumulation of calcium carbonate shells of marine organisms, mostly microscopic plankton called coccolithophores.

Here are some key characteristics of chalk coastlines:

* White cliffs: Chalk is a very light-colored rock, so chalk coastlines are often marked by dramatic white cliffs, like the famous White Cliffs of Dover in England.

* Erodible: Chalk is a relatively soft rock, so it's easily eroded by the sea. This erosion creates distinctive features like arches, stacks, caves, and inlets.

* Biologically diverse: The porous nature of chalk allows for the creation of habitats for a variety of marine life.

* Low-lying cliffs: Chalk coastlines often feature lower cliffs compared to other types of coastlines due to the soft nature of the rock.

Here are some examples of chalk coastlines around the world:

* The White Cliffs of Dover, England: This iconic landmark is a prime example of a chalk coastline.

* The Jurassic Coast, England: While the Jurassic Coast is known for its diverse geology, it also features stretches of chalk cliffs.

* The Normandy Coast, France: This scenic coastline features chalk cliffs and a variety of other geological formations.

* The Baltic Sea Coast: The Baltic Sea has several chalk coastlines with unique features like the Møns Klint cliffs in Denmark.

Chalk coastlines are visually stunning and ecologically important, but they are also vulnerable to erosion, particularly with rising sea levels and changing weather patterns.