Chemical data obtained from the WWWeb.
The interactive Periodic Table at this site is one of the best available on the WWWeb.  In fact, This site contains links for all kinds of "interactive"Periodic Tables.
Here's another - this Periodic Table is maintained by folks at MIT.

Here is a great link for calculating mineral formulae from microprobe analyses, using a series of Excel spreadsheets. The spreadsheets are free and downloadable.

There are many others - in all languages - and with slightly different emphases.
A word of caution: some contain erroneous information - so - BEWARE.