[Clayart] Sand

[ronroy at ca.inter.net]

Great info Joseph, as usual.

If the grains of sand are rounded - as in Ottawa sand or beach sand or  
desert sands - they are not a problem for silicosis because the edges  
are not sharp.

Crushed silica on the other hand has very sharp edges and can cut  
lungs and lead to silicosis.

Best to assume all the silica you meet is the sharp kind.

RR


Quoting Joseph Herbert <josephherbert827 at gmail.com>:

> Hello,
>
> First, ?sand? is a particle size designation that says nothing about
> composition.  There are five divisions of sand size in the Wentworth Scale
> - very course to very fine, 1-2 mm to 0.0625-0.125mm . Sieves 10 through 18
> comprise very course sand and sieves 120 through 230 for very fine.
>
> Natural sands, especially finer sizes, tend to be largely composed of
> quartz (silica) because quartz is so hard.  Other rock forming minerals are
> not as hard or as immune to chemical weathering as is quartz.
>
> There are notable exceptions, like the green olivine beaches in Hawaii and
> rutile sands mined as titanium ore. So ?sand? can have nearly any mineral
> composition.
>
> A famous high purity silica sand is from Ottawa Illinois where the St.
> Peters sand stone is mined and processed.  The sand grains are very
> rounded.  According to some sedimentologists, this roundness and the
> absence of other composition particles indicates a long distance of travel
> from the parent igneous rock.  Perhaps these grains from the St Peter
> sandstone were previously deposited in another sedimentary rock, re-eroded
> (maybe more than once), and deposited as the St Peter.  This idea derived
> from the estimated distance of travel for the rounded grains being
> significantly farther than the length of any existing rivers.
>
> Conversely, sands found near their source, like beach sands of the Great
> Lakes, will have many non-quartz grains present making them more
> interesting for some purposes.  Fatally flawed for others.
>
> One of our correspondents described ?cubic? grains of quartz.  Quartz is in
> the trigonal crystal class and displays no cleavage.  Conchoidal fracture
> is typical in broken quartz crystals, looking much like broken glass.
> Equant grains, perhaps; cubic grains, like table salt, no so much.
>
> Because many sand suppliers only care about the size of what they sell, the
> user needs to be more aware and demanding to get sand that meets their
> needs.
>
> Joe
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Ron Roy
ronroy at ca.inter.net
Web page ronroy.net