BH250-258
Title
BH250-258
Subject
Flint, Chert
Description
Flint, Cryptocrystalline quartz, Microcrystalline silica, Chalcedonic silica, Fine-grained silica
The flint associated with the Brighton chalk is a variety of chert composed primarily of microcrystalline quartz (SiO₂). Although flint and chert are essentially the same siliceous rock, the term flint is traditionally applied to dark, dense chert occurring as nodules or bands within chalk and other limestones. It is considerably harder and more resistant to weathering than the surrounding chalk.
The flint formed during diagenesis, after the calcareous sediment accumulated on the Cretaceous seafloor. Silica derived largely from marine organisms, particularly siliceous sponges and microorganisms, dissolved in pore water and migrated through the sediment before precipitating as microscopic quartz. This process produced irregular nodules, continuous bands and branching forms that may preserve ancient burrow systems.
Weathered flint commonly develops a pale gray or white outer layer called a cortex or rind. This porous layer forms near the boundary between the flint nodule and the surrounding chalk, where silicification was less complete and microscopic carbonate or pore spaces may remain. Exposure to groundwater and surface weathering can dissolve the residual carbonate and further lighten the rind. The boundary between the pale cortex and the dark, dense interior is often sharp, emphasizing the original shape of the flint nodule.
The flint associated with the Brighton chalk is a variety of chert composed primarily of microcrystalline quartz (SiO₂). Although flint and chert are essentially the same siliceous rock, the term flint is traditionally applied to dark, dense chert occurring as nodules or bands within chalk and other limestones. It is considerably harder and more resistant to weathering than the surrounding chalk.
The flint formed during diagenesis, after the calcareous sediment accumulated on the Cretaceous seafloor. Silica derived largely from marine organisms, particularly siliceous sponges and microorganisms, dissolved in pore water and migrated through the sediment before precipitating as microscopic quartz. This process produced irregular nodules, continuous bands and branching forms that may preserve ancient burrow systems.
Weathered flint commonly develops a pale gray or white outer layer called a cortex or rind. This porous layer forms near the boundary between the flint nodule and the surrounding chalk, where silicification was less complete and microscopic carbonate or pore spaces may remain. Exposure to groundwater and surface weathering can dissolve the residual carbonate and further lighten the rind. The boundary between the pale cortex and the dark, dense interior is often sharp, emphasizing the original shape of the flint nodule.
Coverage
Brighton United Kingdom
GPS Coordinates: 50°48'15.09"N, 0° 3'49.71"W
GPS Coordinates: 50°48'15.09"N, 0° 3'49.71"W
Date
August 2025
Creator
Bereket Haileab
Source
SourceFrom the rock collection of Bereket Haileab. Sample BH250-258. Housed at Carleton College in Minnesota.
Publisher
Bereket Haileab
Contributor
Bereket Haileab
D. Haileab
F. Kaleab
D. Haileab
F. Kaleab
Relation
Citation
Bereket Haileab, “BH250-258,” BH250 Mineralogy Teaching Collection, accessed October 22, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/374.