Spontaneous Generation is life from lifeless material. Spontaneous Creation is when an object is formed from nothingness. A setting can have spontaneously created items that are magical, mundane or both. Sometimes this is the result of divine intervention but usually it is a side effect of natural and/or supernatural forces interacting. It could be the result of planar blending, magical storms slamming into each other, cracks in reality splitting open or the creation or destruction of a world. Or just about anything else you can imagine. Resulting magical objects could be considered artifacts, though the majority will be rocks or simple shapes that have random powers, the result of complex forces interacting. If one of the forces that help create the object is a world mind (or something similar), then the object will probably have a specific shape and expected powers. Even those that are just shapes can still be used by characters- they just have to learn how to activate the artifacts' hidden powers. In many cases, these artifacts are non-unique as they are a result of interactions that can happen multiple times, even if it takes a few thousand or million years for the exact same conditions to repeat.
Here are some examples of artifacts that are meant to be rocks or other shapes and are non-unique. Unlike tha artifacts in 2e The Book of Artifacts, these don't have discrete powers. Rather the owner tells the artifact what they desire and if the GM okays it, the result happens. Usually there is a downside or curse involved as well (with a duration determined by the GM).
Pandora's Box (the name of the oldest known version of this catagory) could make an interesting last ditch artifact. When it is opened or activated, the wielder and everyone within 500' are affected by a curse. The weilder just hopes for a less terrible curse than the others affected. Each box could have a significantly different chart of curses it inflicts. Boxes are formed when chaos bleeds through reality and forms a clot, one usually small enough for a human to carry, but some can be up to planet sized. Woe to the people who live on one is the secret of activation is discovered.
A Forest Splinter is the result of green magic or energy having a spasm when reacting to contact with positive and negative energy infused planes. A splinter can be used to create any effect that is possible for druid magic (and thus can differ in different planes). The downside is the resulting forest. A massive overgrowth occurs centered on the splinter that can be 4d6 X 100 yards (or miles) in diameter. The wielder of the splinter is no immune and may even be crushed by the resulting plants or herbs.
A Skeleton Key is the result of divine divination magic interacting with abjuration magic that attempts to hide a world changing secret (in other words, a powerful god trying to break another's attempts at hiding some information). It can be used to open any mortal created lock, but in doing so it also causes all nearby (1000') locks and barriers to fail even if that would be harmful to the wielder.
Mind Stones allow their wielders to use any psionic effect that is possible. Doing so disrupts minds, causing all sapient creatures within 5d6 X 20 feet to lose their ability to reason (INT 2) for a few days or weeks.
Shadow Lenses give their owners the ability to manipulate light in a grand fashion. Vampires and other undead hate them for obvious reasons. The downside is after the effect ends, a large area (5d20 X 100 yards) is cast into shadow and even those who can normally find their way without sight can easily be lost.
All such artifacts should be relatively easy to destroy, possibly as simple as a Disjunction spell, though with the danger of using that spell remains. If one is destroyed, apply its curse one last time.
