I agree - it would seem to be natural that a waste material would be
pressed into use elsewhere, perhaps as a filler for a potting clay which
was used for 'rough' work. Certainly, crushed pot is mixed with clay to
produce a stronger resultant pot-material (called 'grog,' i believe).

In answer to the question, simply put - NO...

The flint-chert found in the plateau grvels is generally brown to white. If
you build a fire on this (dangerous! the pebbles explode quite violently.),
the brown chert turns bright red (Iron Fe(OH)3 --> Fe203& so on). 

The Black cherts tend to contain a quantity of organic compounds (plus
iron) - Occasionally pink and purple cherts are found (usually organic
inclusions, sometimes manganese) etc.

Black chert tends to weather to brown or clear-white (somewhat translucent)
- but VERY slowly. It loses some hardness in the process.

The opaque-white material is usually full of inclusions (carbonates, air
etc, is sometimes ochre-brown etc. from clay, and usually has an earthy or
dull appearance. It can be extremely soft.

There are occasional occurances of almost-transparent, slightly coloured
cherts. These are hardest (H 6.5-7), passing through the black,
brown/clear-white (H 5.5-6.5) and opaque-white etc. (which can often be cut
with a hacksaw, due to the sponge-like structure)- ultimately, you end up
with marl-like rocks being mainly limestone with a cherty content.

As a _general_ rule: where fossil material is included in chert-beds, the
fossils tend to be replaced by a quantity of chalcedony (anisotropic under
crossed nicols), and the bulk of the growth around them is chert (isotropic
under x-nicols). Occasionally small veins of crystalline quartz are found,
too.

Small chalcedony and quartz geodes are not uncommon on flint-beaches (I
have one 10mm wall thickness (flint), 2mm quartz layer, 65mm cavity, along
with several smaller geodes featuring thick flint-wall cavity lined with
brown, white, pale-blue & pale-purple chalcedony). 

Apropos of nothing: Question - are these, strictly speaking, geodes?

For information, on the finding of cherts and chalcedonies on convenient
beaches:
(Apologies for instructing an ancestor on the method of ingesting bird-ovae
:)

Brown and Black flint-chert is found around chalk-outcrops - but the brown
turns up on almost every beach in Britain. Clear amber-brown, blue, purple,
white (the hard stuff, in other words) can be found on beaches close to
Jurassic deposits (The Lias is best for these). Another cherts are found in
the Carboniferous Limestones, and are usually an oily-black. Other
chert-beds exist throughout the Geological series, so be warned.

Dense, hard quartzites turn up on southern beaches with great regularity,
and might be mistaken for chert. They are hard and almost glassy when
wave-polished. Careful examination will show the sugary texture of Sarsen
(fossil forest hard-pan!)


On the subject of the glass - simple flint-glass de-vitrifies rapidly in
contact with chalk-soils, producing an attractive, irridescent mica-like
substance. Depending on the chemistry and water-content, the colours are
generally blue-green but can also be yellow or even red. Victorian
bottle-glass has been found at Petworth (Sussex) de-vitrified to an
estimated depth of 1-3mm!

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----------
> From: Evan Price <[log in to unmask]>
> To: mining <[log in to unmask]>
> Subject: chert
> Date: 09 August 2000 18:35
> 
> Thank you, Paul!  Now, one very unhistorical observation and one further
> question.  The use of chert in making potterty would appear to be a
> natural progression from chipping it to make tools.  The question is: Is
> all chert of a standard hardness and composition?  The chert we
> encountered was a glassy black, but I have seen arrow heads that were a
> brown colour.
>         I can certainly see its usefulness in glass making and glazing.
> 
> 


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