LEGO Dark Stone Gray Rock 4 x 4 x 1.6 Bottom with Transparent Neon Orange Marbeling (30294 / 53934)

LEGO Dark Stone Gray Rock 4 x 4 x 1.6 Bottom with Transparent Neon Orange Marbeling has been used in at least 8 LEGO sets over the past 19 years, since it was first used in 2005. You can also find this part in at least 2 other colors. It has a design ID of 53934 which can usually be found molded into the bottom of the part.