Most meteorites are darker than this specimen, having a characteristic ablation texture on the unfractured surfaces. Admittedly, this specimen is weathered, which could lighten the surface appearance, but it has such a heterogenous texture, including non-spherical vugs, that it looks to me to be more volcanic than meteoritic in origin. The fact that it is strongly ferromagnetic, and smelling of sulphur, leads me to suspect that it might even be slag from an iron foundry - it has the right kind of internal texture. There are strongly magnetic meteorites, largely made of Ni-Fe alloy, but they definitely do not have such a porous texture, are not sulfurous, and would weather to a more reddish colour (from haemetite). I do not believe that this is as hard as diamond, which makes me doubt your quartz-dealers credentials! Summary: either artificial slag or a bit of weathered lava.
BTW: I don't know where 'ghost' is from, but if you ever get the chance to visit Vienna, I strongly recommend the meteorite galleries in their natural history museum - probably the world's best collection of meteorite specimens, of all varieties. Spend a day there, and you will definitely have your eye trained to spot real meteorites.