Throughout the generations, there have always been pokémon that supposedly originated in space: Clefairy, Lunatone, and Beheeyem, for example. Surprisingly, Minior is not one of these extraterrestrials: it did not come from space. Instead, according to the pokédex, it is formed inside the atmosphere.
Strong impacts can knock it out of its shell. This Pokémon was born from mutated nanoparticles. (Moon: Meteor Form)
Originally making its home in the ozone layer, it hurtles to the ground when the shell enclosing its body grows too heavy. (Sun: Meteor Form)
The ozone layer is in the stratosphere, the second layer in Earth’s atmosphere, from around 10-50 kilometers above Earth’s surface. Many airplanes fly in the stratosphere: it’s hardly considered outer space.
Still, Minior is classified as the Meteor Pokémon, so if it’s not from space, what makes it a meteor? The definition of a meteor is “a small body of matter from outer space that enters the earth’s atmosphere.” Generally, they are debris from a larger celestial body, such as a comet, asteroid, or planetoid, that crossed Earth’s orbit some time ago. Earth runs into the debris stream, picking up the particles in Earth’s atmosphere. The friction between the object (a meteoroid) and the atmosphere causes the object to burn up, manifesting itself as a shooting star (a meteor). The few that make it to the ground are called meteorites.
Minior isn’t from outer space, so by definition Minior is not a meteor. Instead, Minior is a precipitate, a dust particle floating in the atmosphere that clumps together with other particles to grow. Rocky precipitates like Minior are often the seeds for rain clouds (see Bronzong for more detail). However, instead of collecting water until it gets too heavy to stay in the air, Minior collects other dust particles in its crust until it is too heavy to star in the air.
Interestingly enough, volcanic activity (found in abundance in the Alola region), can add very specific types of precipitates to the atmosphere: the colorful sulfates, or chemicals with at least one sulfur atom and 4 oxygen atoms. Here are some examples:
(From left to right: Cobalt Sulfate, Ammonium-Cerium Sulfate, Nickel Sulfate, Iron Sulfate, Copper Sulfate, and Chromium Sulfate)
The cores of Miniors, then, are likely different kinds of sulfates! The crusts can be anything and everything else it picks up along the way: clay, soot, dust, pollution, all which are very common in the atmosphere everywhere in the world.