I've been considering filling my alien world with a plethora of magnetic creatures, all of which use magnetism in unique and creative ways. Of course these creatures are only going to be one genus, but still I'd be interesting to see. These creatures have hard metal coatings like scaly-foot gastropods, critters that are mentioned in every single metal creature question on this site. These ferrous exoskeletons initially serve as defence against predation but allows some creatures to exploit magnetism. At some point I came up with the idea of an alien coating itself in magnetite sand (ironsand) and using it as a first line of defence, the exoskeleton being the second.
It is typically dark grey or blackish in colour. It is composed mainly of magnetite, Fe3O4, and also contains small amounts of titanium, silica, manganese, calcium and vanadium. Ironsand has a tendency to heat up in direct sunlight, causing temperatures high enough to cause minor burns.
Slightly burning the mouth of predators is fun and all but if faced against an armed human, like poachers for example, how good would this defence be? Sand being hard to compact makes for a very good shock absorber. As proof of this sandbags are often used in military context.
The theory suggests that about 3 and 1/2 inches of sand would be all that is required to stop a bullet since the standard distance between two pieces of drywall is about 3 and 1/2 inches.
How good of a defence is this sand coating really? How does it fare against armed men? What about primitive hunters? Natural predators?