Isolynium was a rare element with the atomic number 178 on the periodic table. (DIS: "Species Ten-C") When in its most common mineral configuration, it had the same metallic luster as pyrite and equant crystals. It was critical to the creation of isolytic weaponry and was sold on the black market. Unscrupulous dealers usually adulterated isolynium with sammonium, which affected its opacity and shape. A tetryon dosimeter could be used to measure its potency.
In 3190, Doctor Ruon Tarka and Cleveland Booker needed isolynium to construct an isolytic weapon capable of destroying the Dark Matter Anomaly. While Starfleet Intelligence had identified four vendors with access to isolynium, Captain Michael Burnham realized that Booker would likely approach Haz Mazaro to obtain it instead. She attempted to purchase Mazaro's stock herself to deny it to Booker, though she ultimately lost it to him in a game of Leonian poker. However, she had anticipated her loss and hid a tracker on the isolynium beforehand. (DIS: "All In")