Glassy and vesicular = Slag
...especially if there are metal blebs
After iron oxide concretions and nodules, the most common type of meteorwrong that we encounter is industrial 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.
Two other common characteristics of most slags are that they are glassy (vitreous) and contain of vesicles (trapped gas bubbles). Many slags also contain iron metal from inefficient separation of metal from ore during smelting and, thus, they will attract a magnet.
Slags catch people attention because of their morphology. 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 are more common than one might think.
I have not personally examined all the examples pictured here, but I suspect that nearly all 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 natural volcanic rocks. None of them are meteorites, however. None have fusion crusts!
Curiously, quite a few of the rocks that people describe as “it wasn’t there yesterday” look like slags to me.
