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feldspar substitutions. think...natural eutectic melting !

updated wed 5 apr 06


Ivor and Olive Lewis on tue 4 apr 06

Dear Steve Slatin,

Regarding the nature of Nepheline Syenite. I believe I have mentioned =
before that it is possible samples of this Rock to mimic Pearlitic =
Structures in Carbon Iron Alloys, though Geologists call it a "Perthite" =
structure. In the metallurgical case, the structure is a Eutectoid. It =
is created during a solid state reaction as a Carbon Iron Solid Solution =
cools. When the Proportion of Carbon in the alloy is 0.80% an intimate =
mixture of Iron Carbide and pure Iron crystallise together in parallel =
sheets. The lowest temperature for this to happen is called the =
Eutectoid Point.

Since there is such a strong similarity between the two processes of =
formation, it seems reasonable by analogy to infer that Nepheline =
Syenite is a Natural Eutectic Composition.

In the case being discussed, Form may be more important than Content.=20

Best regards,

Ivor Lewis.
South Australia.

skiasonaranthropos@FSMAIL.NET on tue 4 apr 06

Hello Ivor,
Whilst I can not comment about iron alloys could you expand upon why you
consider that a nepheline syenite could be a eutectic composition? Is this
just you submitting it for consideration, and no criticism with that, or
have you supporting references to any studies

The use of eutectic compositions is not unusual in ceramics, such as
purposely mixing a feldspar with a little of what is known as an auxiliary
flux. The respective typical mineralogies of the two main sources of
ceramic grade nepheline syenite are:
orthoclase, or microcline, at 41 & 21
albite at 21 & 53
nepheline at 38 & 26

Do you think eutectic exists with such different ratios? Elaboration on
your hypothesis would be interesting. Of course access to pure nepheline
and feldspar would allow a small trial ... something close to a feldspar is
relatively easy but nepheline?