Refer to the photo. The black centimeter cube is shown for scale and is not included. You are purchasing a display like the one shown. The display box measures 3 x 4 inches. Note, the appearance of each piece of trinitite is unique, so your specimen may vary slightly from the one shown.
A few more words about the safety and legality of Trinitite :
All of the most harmful radioactive materials in Trinitite have long since decayed into less-harmful decay products. For example, when fresh (right after formation), this material was "hot" with trace amounts of Plutonium. However, the hot isotopes in Trinitite have a short half-life, and after 50 years it is safe to responsibly own.
I keep my personal specimens in sealed acrylic gem jar or Riker boxes in my specimen cabinet. Do not handle it, and if you do, be sure to wash your hands afterwards and don't do anything that might crumble or break the Trinitite which could release dust.
Just to be clear for everyone - it is legal to own this material and it is legal to sell this material. It is also legal to ship small quantities of trinitite inside the US. It is *not* legal to go to the Trinity site, hop the fence, and dig up more material. All of the Trinitite on the market was gathered before the prohibition.
CAUTION - Keep trinitite away from children, pets, or curious hands. This is considered a collectible for advanced mineral collectors of radioactive ores and related materials.