Chalk rocks 2: Flint

The shallow tropical Cretaceous seas in which the Chalk formed was home to a rich sea-floor biota, including many siliceous sponges. These have small needle-like spicules which lock together to form scaffold structure made of SiO2 - the stuff of quartz. The amorphous form of silica which forms sponge spicules is quite unstable outside the sponge body and the spicules of dead sponges will dissolve into sea water. As the sediments lithify the silica precipitates out to form flint. It has an extremely small grain size - it is cryptocrystalline (almost still amorphous) and because of this it shows very nice glassy conchoidal fracture behavour. Because it precipitatied from a fluid, the flint takes on the form of the cavity which the fluid was occupying and so flint casts of fossils are quite common.
See also:
Chalk rocks 1: Chalk
• Chalk rocks 1: Chalk
Chalk rocks 3: Marcasite
• Chalk rocks 3: Marcasite

[@blueskiesparagliding1078]

Mystery Solved, thank you I've tried finding an answer for this in other places but it ended up making my head hurt. Thank you for your very simple and brief explanation 👍

[@OneMinuteGeology]

No worries. Glad you like it.

[@Wonkabar007]

Amazing that a soft sponge can end up forming hard flint

[@OneMinuteGeology]

Yes! But I guess it took many sponges to make a single flint.

[@zainabjaber6800]

Can u write this i can not understand u

[@SardarAli-vb6dz]

plz translation in hindi

[@suhaasajay9176]

👌👌

[@lcfcking9104]

I have found a perfect ball and it has a egg texture..it's insides have chalk look to it I'm putting a video on my account for anyone who has information on it