14. The second book in the series, "The Currents of Space" (1952), takes us to the two worlds of Florina and Sark. Florina has many problems, but it's the sole source of kyrt -- a substance the galaxy doesn't want to do without. What is kyrt?
From Quiz Isaac Asimov's Galactic Empire
Answer:
A fiber based on cellulose
Midway through the book, Lady Samia Fife muses on the miraculous kyrt: "Of course kyrt didn't really shine of itself, but properly spun, it would gleam metallically in the sun in a variety of colors or in all colors at once ... Its fibers could be spun finer than the most delicate synthetics and those same fibers had a tensile strength no steel alloy could duplicate." People have tried to grow kyrt on other worlds, but away from Florina, it grows "white, flat, weak and useless. Not even honest cotton."
Its immensely valuable kyrt crop could have been a blessing for Florina, but instead, the people of that planet are horribly oppressed by the Squires of Sark, and their riches flow to that other world. Until something changes...