Many of the meteorwrongs sent to us are pieces of slag. Slag usually refers to a glassy by-product of smelting ores to retrieve the metal. I use the term here to also include any man-made, rock-like by-product of heating things to high temperature. Thus, clinkers are a form of slag. Slags catch people attention because of their morphology. Many slags contain metal from inefficient separation of metal (above) from the ore and, thus, will attract a magnet. Two other common characteristics of most slags are glassy (vitreous) surfaces and the presence of vesicles (gas bubbles). Slags often have very rough exteriors, unlike any stony meteorite. Some show flow features in the glass and others have flat surfaces from having solidified in a contained space. Slags are sometimes used in road construction and as landscaping gravel, so they’re more common than one might think.
I have not personally examined all the examples pictured here, but I suspect that most are slags. Some might be fulgurites – lithified soil and vaporized organic matter produced as a result of a lightning strike. Some might be products of electric discharges when high-voltage power lines fall to the ground. A few might actually be volcanic rocks. None of them are meteorites, however.