Downed power line by my house makes glass out of the dirt - Page 1
Forum section: electronics / general

author: duckduck
author_rank: Frequent Contributor
timestamp: May 29, 2021, 09:32:18 pm
content: There were strong winds Thursday afternoon. A falling branch knocked down the power lines at the end of my street.I live in the suburban/rural USA and I guess the power lines in my neighborhood are two phase, maybe 4kV?The ground was blackened in a line in places for about 5 to 10 meters where the power line was lying.I picked up a couple of samples from the area. You can see the melted aluminum power lines and glass that the high heat made out of the soil. There were fingers of melted aluminum and "roots" of bubbled glass that ran away from the site for up to 30cm. It smelled burnt. This was the work of a large number of very angry pixies.PP3 and pen for scale.EDIT:Thanks, amyk. Yes, that's exactly what is was like. Tubular glass "roots" in the dirt, and the (previously molten) aluminum was spread out in the surface in Lichtenberg figures. I knew there was a name for those.

author: amyk
author_rank: Super Contributor
timestamp: May 29, 2021, 09:40:17 pm
content: Looks likehttps://en.wikipedia.org/wiki/Fulgurite

author: ChristofferB
author_rank: Frequent Contributor
timestamp: May 29, 2021, 09:43:15 pm
content: That's insanely cool but strange: if this is a glass, the ground needs to be very sandy, and sand probably couldn't carry the current to provide enough heat to vitrify sand into glass - had it just rained? What's your earth like normally?

author: duckduck
author_rank: Frequent Contributor
timestamp: May 29, 2021, 10:05:17 pm
content: Quote from: ChristofferB on May 29, 2021, 09:43:15 pmThe ground was probably a little damp. This was by the side of a road, so sandy soil with crushed gravel. The asphalt road was also burned as well where the line came in contact with it. I think our earth is normally well grounded.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 29, 2021, 10:48:08 pm
content: Doesn't take much sand to form glass, and >50% silica is very typical for most soil types I think? Now, it might not be present as sand, as such (quartz grains of a certain size) -- there's also loam, clay, etc., and all the minerals included therein which contain some silica. And those are mostly due to weathering of surface rocks (particularly feldspars and micas, with quartz, magnetite, olivine, etc. grains weathering more slowly, coming along for the ride).Most soils, after burning out the organics, will sinter into some kind of loose ceramic; it takes a pretty clayey soil (or separation and refining), to get a dense fired body as such. In natural clay deposits, this has been done by nature, usually at the inside bends of former river banks. Or it's weathered in-situ, as some kaolin deposits I think?The main things thatwouldn'tbe silica, are lime (particularly on tropical beaches/islands, below limestone/chalk/dolomite bluffs, etc.), and iron and alumina (which are left after basically everything else weathers out -- it takes a LOT of water to do this, so you get such red soils in semi/tropical areas -- the extreme case of which is bauxite, used for aluminum ore). Alumina doesn't form glasses, or at least so easily, and same for iron. Iron (when it's reduced) and lime are also fluxes, making a softer, lower melting glass when silica is present, or just kind of a jumble of crap I guess if there's really very little silica.Magnesia, iron and alumina tend to form spinels: compounds of the form AB2O4, A being a divalent element like Mg, Fe(II), Zn, etc., B being trivalent like Cr, Fe(III), Al, etc., and O being oxygen. (Ionic radius matters: Ca, Sr, etc. tend not to form spinels.) Plain old spinel (the gem) is MgAl2O4, but each element can be substituted with others (a solid solution), so it comes in many colors. Magnetite is an end member that can be described as ferrous ferrite; electronic ferrites (ZnMn and NiZn) substitute the Fe(II)/Mg with those elements, which happens to enhance the soft-magnetic properties of the Fe(III) atoms.Mind, not that you're likely to see new crystals in such a rapidly cooled, haphazard mess like this -- you'd have to fully melt, and then cool such a mixture probably for hours to weeks, to see much crystallization. Longer for a melt with much silica in it. So, glass is pretty likely here. Generous helpings of iron will cause the dark color.Tim