#### davenn

Science Advisor

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I'm into rocks and minerals but I'm not a chemist

I cant really find a definition between .... chemical formula and Idealised chemical formula ?

example below of a mineral sample I purchased a few days ago

part info from ...

https://www.mindat.org/min-3760.html

**Chemical Properties of Stellerite**

Formula:

Ca4(Si28Al8)O72 · 28H2O

Idealised Formula:

Ca(Si7Al2)O18 · 7H2O

Now, as a non-chemist, I look at that and wonder about the significance between the two formula ?

how can the upper formula be reduced to the lower idealised formula ?

OK, one light just came on as I was writing this ... I note that everything in the top formula has been divided by 4.

So, my Q still remains, does this really affect the composition of the mineral ?

if not, as I suspect, why list it as the first when the second formula can be used ?

Thanks Lots

Dave