Chernobylite is a solid solution compound consisting of a crystalline zirconium silicate and an amount of uranium as high as 10%.
It was discovered in corium (a lava-like glassy material) that was formed during the nuclear meltdown of Unit 4 in the Chernobyl disaster. Chernobylite is highly radioactive due to its substantial uranium content and contamination by fission products, however it is not any more radioactive than the corium itself.
Some yellow, powdery, secondary uranyl phases made up of Studtite, becquerelite and phurcalite that formed on the surface of the corium due to interaction with water are often mistaken for Chernobylite. Those yellow minerals are not chernobylite. Chernobylite cannot be seen with the naked eye as it appears as microscopic crystals that can only be seen using SEM.