I am always on the look out for every day things that can be used in compositions. This is usually the best way to acquire ingredients because they are so cheap... Any more?
Barite is Barium Sulphate. Not sure, but I think this is also brittle and easy to process, and relatively insoluable.
Silicon crystals can be bought from mineral shops. Useful for adding to priming compositions in powder form...
Stock Titanium can be filed into a powder without too much bother. A useful alternative to the expensive powder.
Can't think of any more.