Trinitite, also known as Atomsite or Alamogordo Glass, is the glassy residue left on the desert floor after the plutonium-based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico. The glass is primarily composed of arkosic sand composed of quartz grains and feldspar (both microcline and smaller amount of plagioclase with small amount of calcite, hornblende and augite in a matrix of sandy clay) that was melted by the atomic blast. It is usually a light green, although color can vary. It is mildly radioactive, but is safe to handle.
The glass has been described as "a layer 1 to 2 centimeters thick, with the upper surface marked by a very thin sprinkling of dust which fell upon it while it was still molten. At the bottom is a thicker film of partially fused material, which grades into the soil from which it was derived. The color of the glass is a pale bottle green, and the material is extremely vesicular with the size of the bubbles ranging to nearly the full thickness of the specimen.
In 1952, the site of the explosion was bulldozed, and the remaining trinitite was disposed of. On December 21, 1965, the 51,500-acre (20,800 ha) area Trinity Site was declared a National Historic Landmark district and, on October 15, 1966, was listed on the National Register of Historic Places. (from Wikipedia)