darkSpyro

CHALK-

Chalk /ˈtʃɔːk/ is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert unique to chalk) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint).

Chalk as seen in Cretaceous deposits of Western Europe is unusual among sedimentary limestones in the thickness of the beds. Most cliffs of chalk have very few obvious bedding planes unlike most thick sequences of limestone such as the Carboniferous Limestone or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years.


"Nitzana Chalk curves" situated at Western Negev, Israel are chalk deposits formed at the Mesozoic era's Tethys Ocean
Chalk has greater resistance to weathering and slumping than the clays with which it is usually associated, thus forming tall steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downland, usually form where bands of chalk reach the surface at an angle, so forming a scarp slope. Because chalk is well jointed it can hold a large volume of ground water, providing a natural reservoir that releases water slowly through dry seasons.

Sidewalk chalk are typically large colored (and sometimes white or cream) sticks of chalk (calcium sulfate rather than rock chalk, calcium carbonate) mostly used for drawing on pavement or cement sidewalk. It is sometimes used by children to draw a four square court or a hopscotch board. Blackboard chalk is typically shorter.

There are several different types of sidewalk chalk, typically coming in solid-colored sticks. 3-D sidewalk chalk sets, in which each stick of chalk is created with two particular colors that appear 3-dimensional when viewed through the 3-D glasses that come with the chalk, also exist.[1]

Sidewalk chalk can be cheaply homemade.[2]

Rudy's got the Chalk!

Quote: AvatariDragon

Rudy's got the Chalk!

________

Chalkzone

What happens if you put chalkboard chalk in a bucket of fresh water?

suddenly, shrek.