Rubidium

"If you see purple or red sand, back up. That's rubidium or strontium, and even breathing it can kill you."

―Rey's survival guide^[1]

Rubidium was a purple-colored solid substance. It was poisonous, being potentially lethal to inhale. Rubidium could be used as fuel for vehicles^[1] or explosives, with the use of the substance in the latter leading to explosions with a purple hue.^[2]

In 5 BBY,^[3] Sabine Wren, a member of the anti–Galactic Empire rebel crew of the starship Ghost, noted in^[2] her^[4] journal rubidium as a possible fuel for creating purple-colored explosions.^[2] After^[1] the Galactic Civil War battle on the planet Jakku ten years later,^[4] the planet's surface became littered with the wreckage of starships and vehicles, leading to dangerous fuels such as rubidium leaking in its sand. At some point prior to^[1] her departure from Jakku in 34 ABY,^[4] the human scavenger Rey mentioned rubidium in the survival guide she was writing. She included in it a note with a visual depiction of a sample of the substance and wrote that rubidium colored sand purple, a fact that could inform scavengers to proceed with caution.^[1]

Behind the scenes

A sample of pure real-world rubidium (top)

Rubidium was first mentioned in the current Star Wars canon in Sabine My Rebel Sketchbook, which was written by Daniel Wallace^[2] and published on February 3, 2015.^[5] Rey's Survival Guide, authored by Jason Fry, illustrated by Andrew Barthelmes,^[1] and released on December 18 of the same year,^[6] provided the first visual depiction of the substance.^[1]

In the real world, rubidium is a chemical element and metal with a silvery-white luster and a melting point of 38.9 degrees Celsius (102 degrees Fahrenheit).^[7] It is nontoxic^[8] but it ignites spontaneously in air and reacts violently with water. In nature, rubidium is generally only found as an impurity in other minerals.^[7] It is sometimes used to obtain purple color in fireworks.^[8]