Cob: Blue clay

[Greyraven Shadowalker]

I have what is apparently known (at-least in this
area, N.E. Ohio) as "blue" clay, again as I've been
informed locally the clay is blue from oil content.
I have speculative concerns as to the health and
functionality of creating, and dwelling in, a home
comprise of oil laden clay. 
Are my suspisions well founded or not?
Is the oil content of "blue" clay a petroleum
infiltration, or am I'm dealing with some sort of
flora secretions, or even a "wive's tale"?
Any insight or assistance with my query will be
greatly appreciated. I am eager to begin construction
of my little  cottage, however I fear that
constructing with an oil rich clay might not provide a
solid and heathful structure.
Blessed be,
Grey


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"When I look into the abyss it stares back at me, 
but not as the cold dark beast you perceive it to be.
When I am gazed upon by the abyss I see the eyes of a 
mother, a lover, an old friend.
When I look into the warm familiar eyes of the abyss
I see that which needs me as much as I have need.
I remember, I rejoice, I renew!"

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