Flintstones in chalk?

Question

I find flintstones intriguing. These dark, hard stones in their pale grey skins have had such uses in our past and our present.

I know that chalk is the compressed remains of tiny sea creatures - but can anyone tell me how flint was formed?

Answer 1

The mode of formation of flints is still the subject of much geological debate. Flint is typically formed within chalk, not just on the south coast of the UK but in the chalk of Yorkshire, and in chalk in Europe and the USA. In fact, flint beds are one way of correlating chalk, as a typical bed of flints can extend over hundreds of square miles. Chert is a related form, found within (non chalk) limestone rocks

Flints are a cryptocrystaline form of silica, and the flints are formed chemically within the rock precipitating somehow (the exact mechanism is debated) from groundwater containing silica. The source of the silica is probably the spicules of silicaceous sponges. Flints often fill burrows in chalk, often providing remarkable preservation, I have seen one where you can clearly see the scraping marks of the creature that built the burrow. Flints can also fossilise sea urchins and other creatures and it is possible that some organic factors assist in the silicification process.

The strongly layered nature of other flints indicates that changing oceanic chemistry, possibly reflecting depth changes and termpreature, that would affect the solubility of silica may also be a factor

Answer 2

I bet you are from England. Well, chalk is a form of calcium carbonate, which is also the chemical composition of limestone, marble, corals. the organism that formed the chalk particles were plants, actually. Microscopic plants, though that floated in the surface of the oceans where the accessed energy from sunlight.

the chalk beds took millions of years to form and it then took millions of years for them to be lifted above sea level due to natural forces. In this new environment, they were subject to being a carrier for groundwater. Groundwater can dissolve a tiny amount of silica from other rocks which contain it. Silica is only soluble to 2 parts per million, but over the ensuing millions of years, that silica can be carried in solution until it enters a natural cavity in the chalk and deposits out as flint.

My explanation is very cursory but, truth is, nobody knows how the reaction actually occurred but that is what has happened. Agates form in volcanic rocks, similarly, and precious opals in Australia's sandstone deserts. Flint is crystalline, although cave men valued it for the way they could flake it to create sharp points and edges for cutting and piercing skins and meats. It must have been a very valuable trade item for those who lived on top of the chalk cliffs.