Volcanic ash is rock that has been pulverized into dust or sand by volcanic activity.
In very large eruptions, ash is accompanied by rocks having the weight and density of hailstones. Volcanic ash is hot near the volcano, but it is cool when it falls at greater distances. Ashfall blocks sunlight, reducing visibility and sometimes causing darkness. Ashfall can be accompanied by lightning. Fresh volcanic ash is gritty, abrasive, sometimes corrosive, and always unpleasant.