Its body is a magnetic stone. Iron sand attaches firmly to the portions of its body that are particularly magnetic.
– Pokémon Sun Pokédex
Alolan Geodude is Rock/Electric instead of Rock/Ground. The lore is that it’s become magnetic. The eyebrows and hair on its head are made of iron sand.
The Rock/Electric typing is unique to Alolan Geodude’s family. It’s not a very good type defensively though, being 4x weak to Ground, and still weak to Water and Grass.
Stat-wise, it has the same stats as Kanto Geodude: good Defense and Attack, low everything else (in fact, Alolan Geodude has the lowest Sp Attack, Sp Def, and Speed of all Electric type Pokemon). At least it learns Thunder Punch as a physical electric move; the first Electric move it learns by level-up is Thunder Shock, which is not very useable with its base 30 Sp Attack.