Fulgurite (noun, “FUHL-grr-eyte”)
A glassy deposit that is often in the shape of a tube. Fulgurites are formed when lightning strikes sand, soil or rock. If that surface has a lot of silica in it, the heat and electricity from lightning may fuse it and other minerals together into glass. Silica is a grid made of silicon atoms with oxygen atoms attached, and is used in making glass.
In a sentence
When volcanoes erupt, lightning can heat the volcano’s ash in the air, forming tiny specks of glass. These are similar to fulgurites that form after lightning hits the ground.
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fulgurites Glassy deposits that form in rocks or in sediment when a lightning bolt strikes the ground.
glass A hard, brittle substance made by melting sand (silica) together with lime (a highly alkaline material obtained by heating limestone) and other ingredients, then cooling the mix quickly. Glass usually is transparent and fairly inert (chemically nonreactive).
silica A silicon atom attached to two oxygen atoms. It is commonly found in quartz and crystal, and is used to make glass.
silicon A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.
Edited 3/24/15, 9:39AM ET: The article was updated to clarify the structure of silica.