The name pyrite is from the Greek word meaning fire because of the sparks that result when pyrite is struck against steel. Pyrite or iron pyrite is iron disulfide, FeS2, it has isometric crystals usually appearing as pale brass colored metallic cubes that have earned pyrite the name "fool's gold". Ironically, small quantities of actual gold can sometimes be found in pyrite to the point where the value of the gold in your sign may actually exceed what you paid!
Pyrite is the commonest of the sulfide minerals and is found world-wide. It is found in quartz veins, sedimentary rock, metamorphic rock as well as coal beds. Pyrite is used in the production of sulphur dioxide for the paper industry and in the manufacture of sulphuric acid, though not as much as it used to be.
Now you know, if you're lucky enough to see a piece of pyrite in your Green Slate sign, it's not a flaw.. it could be your own private mini Gold Mine!
Click HERE to see a closer view of the Pyrite slate.