Richard:

Iron slag from Michigan is quite common for ship's ballast.  The hardness
of the blue "glass" matrix should be 8 on the Mohs scale and specific
gravity around 6 if it is Fe slag.

The blue color MAY be from minor amounts of copper if some chalcopyrite was
in the original mix-a possibility if they were smelting pyritic iron
ores-.and a pXRF analysis MIGHT have +50 PPM Cu OR it could be from Co, a
quick pXRF analysis should be diagnostic.

Always, Always, do a simple hardness test and a Jolly Balance Specific
Gravity determination.  The resulting data will, normally, allow a quick
identification from a table in Dana's *Manual of Mineralogy.*

My Two Cents.

Richard J. Lundin, BA, MA, RPA, ISAP, AIPG
Mineral Exploration Consultant, Professional Geologist (AIPG) & Permitting
Specialist
Registered Professional Archaeologist (RPA) & Remote Sensing Specialist
(ISAP) (Airbourne & Archaeogeophysics)
President & CEO, RICH ORE Mining, Inc.
President, Wombat Mining & Exploration Co.
Director, Wondjina Research Institute


On Thu, Oct 6, 2016 at 4:12 PM, Patrick Martin <[log in to unmask]> wrote:

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