Slag from iron smelting. Tons of it at Fayette, Michigan. Colors vary, but blue is common. 


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> On Oct 6, 2016, at 7:01 PM, Richard Wright <[log in to unmask]> wrote:
> 
> Hello
> 
> The other day a blue stone was handed to me for identification. It 
> was found in the intertidal zone in Mort Bay, Sydney Harbour,
> Australia..
> 
> I have never seen anything like it - either from Mort Bay or from
> anywhere.
> 
> https://app.box.com/s/6da0yfp1w9bzaitei347ltogwd1s9rux
> 
> The intertidal zone has gravels that include exotic rocks, such as 
> flint. These are interpreted as discarded ballast from ships. Indeed 
> the point on the other side of the bay is called Ballast Point,
> 
> The blue stone is much abraded, presumably by sand in the intertidal 
> zone. There are what appear to be inclusions of ironstone embedded in
> the blue matrix.
> 
> My provisional conclusion is that it is slag from smelting iron, akin
> 
> to the process that produced the blue slag from Leland in Michigan,
> USA.
> 
> http://mynorth.com/2014/08/leland-blue-a-way-of-life-in-northern-michigan/
> 
> It has been suggested to me on another forum that there are two other
> possible interpretations of this piece of blue stone:
> 
> 1. It is silica that accumulates in the ashes during the refining of
> sugar.
> 
> 2. That some black bottle glass turns blue in patches when subjected
> to fire.
> 
> I am inclined to stick with my provisional conclusion that it is slag.
> This is because of the inclusions of seemingly ironstone pieces
> embedded in the blue matrix.
> 
> Any suggestions will be gratefully received?
> 
> Richard
>