Jamie,
Limestone will not melt under normal pressures, it decomposes into lime
CaO, similarly dolomite dolmite will decompose into CaO and MgO.
My data book gives the melting point of CaO is 2873 degrees K, and of MgO as
3173 K, substract 273 to get celcius temperatures. However, at 1025 atmospheres
CaCO3 will melt at 1612 K. The same book give the decomposition temperature of
calcite as 1172 K. However, work on calcite tempered pottery shows that the
process is dependent on a large number of factors, such as grain size,
aggregate size, minor element composition, etc., in real systems.
To the above must be added that both oxides will react very readily
with any silica present to form lower melting point silicates. The melting
temperatures for these mixtures are given by the equilibrium phase diagrams. In
particular see the series of volumes of Equilibrium Phase diagrams for
ceramists.
As I do not have the composition of that particular gabbro, I can not
give a temperature, but such rocks often have a large gap between there
solidus and liquidus temperatures - that they 'melt' over a range of
temperatures at a given pressure and partial pressure of water. A way of
estimating the melting temperature of the dry system is to look at the minerals
present and determine which equilibrium phase best fits the mineralogy. Then
from the average composition determine the melting point.
On Fri, 10 Nov 2000 15:08:08 -0400 "J. H. Brothers" <[log in to unmask]> wrote:
> I realize that fluxing is a chemical and not a thermal reaction. But does
> anyone happen to know the melting temperature for limestone? Nahant Gabbro?
> Dolomite?
>
> Thanks
>
> Jamie Brothers
>
>
Chris Salter
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