In scientific terms, chalk refers to a soft, white, porous sedimentary rock that basically forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores. Continue reading for eighteen examples showing what geeks can do with this rock – bonus Chalk Warfare videos included.
- Chalk is composed mostly of calcium carbonate with minor amounts of silt and clay. It is normally formed underwater, commonly on the sea bed, then consolidated and compressed during diagenesis into the form commonly seen today. During diagenesis silica accumulates to form chert or flint nodules within the carbonate rock.
- Ninety million years ago the chalk downland of Northern Europe was ooze accumulating at the bottom of a great sea. Protozoans such as foraminifera lived on the marine debris that showered down from the upper layers of the ocean. Their shells were made of calcite extracted from the rich sea-water. As they died a deep layer gradually built up and eventually, through the weight of overlying sediments, became consolidated into rock. Later earth movements related to the formation of the Alps raised these former sea-floor deposits above sea level.
- Chalk is used to make quicklime and slaked lime, mainly used as lime mortar in buildings. In southeast England, Deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps the most famous is the extensive complex at Grimes Graves in Norfolk.