Pyrite is a very nice mineral and it can be found in the east of the Netherlands. A while ago I've gone to the quarry that is open to the public, shown in figure 1, and I've searched there for pyrite (and other stuff ofcourse).
Figure 1) Pyrite quarry in Winterswijk, the Netherlands.
I took some of the big pieces I found there back to my house for further research. (See figure 2.) I will show you in this article how to get the pyrite out of the rocks.
Figure 2) Pyrite containing rocks.
Using a hammer and chissel, it's possible to break up the rocks. You are looking for gold shiny pieces of pyrite, sticking out of the sides of the rocks. Pyrite is a brittle metal, so be carefull and don't chissel to close to the crystals. The layers of limestone are easy to remove, but the pyrite is embedded in a harder type of limestone. Use natural cracks in the rocks to split them open. See figure 3 (still to come) for some of the results.
The pyrite is still embedded in a stone matrix and this has to be (partially) removed to show the crystals. There are multiple methods to do this and I will show you two of them.
Pyriet is ussually embedded in limestone or varieties of it. Limestone can be dissolved in weak acids (like vinegar) and pyrite won't. So put a few pieces of rock in a cup of vinegar and let is sit for a while. See figure 4 and 5 (still to come) for the results. Normal vinegar will do, but cleaning vinegar has a higher pH (it has a higher level of acidity). Both vinegars are not toxic, but with long exposure times you will need to wear gloves. It's also a good thing to wear eye protection and cleaning vinegar is not meant to be swallowed. (It can contain methanol.)
Figure 6) Microscope image of a pyrite crystal.
Figure 7) Microsocpe image of an iron crystal.
After the acidic bath there will be undissolved pieces left. Under the microscope you can see small quartz, pyrite and iron crystals, see figure 6 and 7.
If the pyrite is not embeded in limestone, than it will have to be treated manually. The stone around the crystals can be removed with small chissels, hammers, even tendist tools. Files, preparationneedles are also usable, a lot of patience is absolutely necessary. See igure 8 en 9 (still to come) for the results. Keep in mind that its possible that there is pyrite underneath the stone your trying to remove, so be carefull not to damage any hidden crystals. And ALWAYS wear eye protection, for stone splinters can be very sharp.
To be continued...
 Photos from my personal collection.