I'm assuming the "selected other quests" involve ones that include an optional rewards slot with a stack of 4 or 5 gems.
Not necessarily. Many quests have gems as an optional reward, but not all of those have malachite among the gemstone candidates.
Yeah, but most quests I've completed so far have 1 or 2 gems available, and despite a lot of reloading, never saw Malachite. Mind over Matter had a stack of 5 gems in one of its slots, and it turned up Malachite twice.
Since reloading to finish that quest multiple times also gives the lesser reward for just Valeri's segment of it (including a slot with 1 gem), and I never saw Malachite in it, I'm guessing only quests with stacks of gems greater than 2 have Malachite randomly.
