This is what happens when sand gets struck by lightning!
Fulgurites are natural hollow glass tubes formed in quartzose sand, silica, or soil by lightning strikes (at 3,270 °F), which instantaneously melts silica on a conductive surface and fuses grains together over a period of around one second.
The following pictures are of a man-made fulgurite that was created when a high voltage power line fell during a windstorm, and then continued to arc to the ground for a couple of hours. When a high voltage power line initially contacts the ground, it begins arcing. The intense heat of the arc and the high current flowing into the ground cause sand, rocks, and minerals in the soil near the line to fuse into a glassy, lava-like substance. A couple of video clips showing downed power lines arcing to the ground can be seen here
(Note the power hum. Wow...). In the latter video clip, the molten region of soil near the downed line can clearly be seen glowing for quite some time even after power was turned off. For a variety of technical reasons, downed power lines may remain energized for quite some time before the power company detects the problem and kills power to the circuit. Even worse, automatic "re-closers" may temporarily cut off power for a few seconds, and then reapply it with no warning. This sequence may repeat several times before the re-closer locks out and must be manually reset. During the brief dead times, people nearby may think that the line is safely dead, and may get injured or killed when power is suddenly reapplied.
Since molten minerals are excellent electrical conductors, the current-conducting area around the line continues to expand and glow as electrical power continues to flow into the ground fault. Once power is finally removed, the molten materials solidify into a bubbly, glassy "rock", leaving a man-made "fulgurite" behind. Unlike natural fulgurites, those created by a downed power lines tend to be considerably thicker and more massive. Linemen sometimes call these curious artifacts "clinkers" because of the ringing sound they make when struck. As with natural fulgurites, clinkers are often hollow with polished, glassy interior walls. However, because they're thicker, they tend to be considerably heavier and massive than the thin, fragile lightning-created fulgurites which are created within a fraction of a second.
These pictures are of a clinker that was formed in Northern California in 1994 when a 7,200 volt power line fell onto a pile of clam shells next to a canal in Hickman, California. Although this 28 inch long specimen weighs about 80 pounds, it is actually only a small piece of the 15 foot long clinker that was created. Shell fragments can be seen embedded in the exterior of the glassy walls.