A normal impact crater
Meteors can be found in mystcraft worlds as a result of severe instability (e.g. Dense Ore worlds) or by adding the "Meteor" page to a descriptive book.
Their impact is reminiscent of a small nuke going off, creating a crater with a diameter of approximately 20 meters in a stone surface. Also large portions of the crater will be briefly set on fire, possibly causing bushfires in forests. An impact in water will cause the crater to be generated at the bottom of the water body, however the water on top of that crater will also have a significant hole on it.
They can be seen if the player keeps an eye on the sky, they also give off a warning sign, if you see a long black "thing" going to the ground, that area will be hit by a Meteor if you get near it. They can strike in the same place twice so be careful.
An impact in water
Even a Cave World will take significant damage after long periods of time, as the meteors constantly erode the surface and after as little as a few hours penetrate the "ceiling" of the cave world and bombard everything underneath.
A Cave World after several hours of bombardment.
In the post-explosion ores such as Gold, Coal and Iron are left exposed in the blast radius and can also be found in trees, as they can travel several dozen blocks from the original impact.
The health damage from an explosion is exceedingly high, meaning that more basic types of armor are nearly useless against it. A Nano Suit gives some level of protection, so does a Hazmat Suit (though the Hazmat Suit loses 99% of its durability), however the player is hurled so far in the air that he usually dies from fall damage unless wearing a jetpack.