Rock Humans are creatures that evolved with silicon as the element they are primarily composed of. Silicon-based life appeared at the same time as carbon-based life. Both kinds of organisms evolved at the same time, although silicon-based cells were fewer in number.
Sleep hits suddenly at different times depending on the individual and will last anywhere from 30 to 90 days but after waking up, a Rock Human won't sleep again for at least two months. While hibernating, breathing is halted, though a small amount of skin respiration is required through the cracks found on their outer layer. If necessary, they can stay in hibernation for 25 years and sustain temperatures as high as 950 °C and as low as -240 °C. Their body heat, as well as scent, disappear while dormant causing various fungi, moss and even pearls to grow on their body.
The means by which they harden into stone involve an intricate cell system that stores moisture within the interior of each cell and is protected by carbon-rich cell walls. Any item a Rock Human carries when he's hibernating will be covered with a hard membrane which tears off like a scab upon awakening.
When hibernating, Rock Humans will prefer places such as shrine grounds, parks with statues, gardens of expensive houses, and underneath maple trees with squirrels in them. They will generally avoid sleeping in areas that were previously flooded, or have high chances of being rained on by tree sap or bird poop.
There are both male and female Rock Humans who procreate and give birth much like humans. Visually, there are no differences between them and humans, though their skin upon awakening appears slightly moist, damp and erotic. Male humans and female Rock Humans can interbreed, but there are no examples of the vice versa.
Rock Human mothers give birth in the spring and summer seasons and carry the fetus for six months. On average, newborn babies have a length of 28 millimeters and weigh 15 grams, keeping that form for seventeen years. It is believed that Rock Humans can live for 240 years. When a Rock Human dies, it leaves no corpse, as it crumbles away into rocks.
Rock Humans eat plants, fruits, nuts, meat, fish, and all other forms of life. They enjoy honey, and all are allergic to mangoes.
Rock Human mothers almost never have affection for or a parental relationship with their child. Soon after birth they take their child to a forest and place them in the roots of a dead tree.
After being left by their mother, a Rock Human baby will wait to be attacked by a wasp, which they will latch onto and use as transportation to a hive. They transform into stone mid-flight while getting covered with pheromones so the other wasps will not see them as food. After reaching the hive, they roll their stone bodies until they find the queen. The babies then dig into the softest part of the queen's body and climb in, effectively riding the queen's body with only half of themselves left alive. They will then learn by themselves the laws of nature, the flow of time, the concept of numbers, and how to live in a group. They wait 17 years for their first "molting", at which point they will venture to the outside world after killing all of the wasps.
Rock Humans' actions are fundamentally independent and they have no families, but they will sometimes form groups for self-benefit and infiltrate human society. However, they don't form any relationships beyond "give and take" ones. That said, it is shown that Yotsuyu Yagiyama and Aisho Dainenjiyama had some bond together, as Yotsuyu saved Aisho from drowning and empathized with him when he lost his house and was betrayed by his girlfriend; likewise Aisho was angered that Yotsuyu had died and considered him a comrade. The A. Phex Brothers were also quite attached to each other as siblings.
They hold a certain reverence for the power found within the Earth and nature. As they are fundamentally able to live through weather changes, they require no assets such as a house or land. They like to make places that give humans special powers their "true home".
With the natural nature of humans spreading and migrating across the continents and their continuous migration to this day, Rock Humans are unable to safely coexist or mutually understand human society. With their natural environment slowly being taken over by human development, some have taken the form of "parasites" by falsely entering the family registry system to maintain property and assets. However, due to their extensive hibernation, Rock Humans cannot go to school or hold regular jobs, instead working in occupations that allow irregular business hours. Rock Humans also rarely fall in love with normal humans, but if they do, there's a 97.5% chance it will end in disaster. The breakups between humans and Rock Humans are said to end in someone's murder.
Abilities and Powers
Rock Skin: Presumably separate from hibernation, each Rock Human has the ability to shift their outer appearance from a normal human into a rock-like state and vice versa at will. In their rock form, they are able to camouflage into their surroundings, and improve their durability to some extent. The ability to stay human requires some type of focus however, as Aisho describes his rock form as something he was born with, but unable to control at a younger age. Yotsuyu, who is presumably more experienced in controlling it, is able to revert to human, rock, and a hybrid where he can still move despite having a rock-like appearance.
Stands: 95% of Rock Humans possess Stands. The reason for the high proportion of Stand users in their population is likely due to them living in "special places" including the Devil's Palm and near the Wall Eyes in Morioh, which are locations known for being able to grant Stand abilities.
The typical behavior of some Rock Humans involves assimilating into human society to the best of their ability, while maintaining secret contact with small groups of other Rock Humans, two of which serve as collective antagonists of JoJolion.
Led by Tooru, this group of Rock Humans prioritize gaining the power of the New Locacaca's equivalent exchange, and to secretly obtain and sell Locacaca fruits for wealth.
Within the organization is a small faction led by Tamaki Damo, dedicated to smuggling Locacaca plants overseas via members sneaking onto cargo vessels and hibernating for the duration of the voyage. The fruits would then be harvested and sold to customers in need of their equivalent exchange property at a lofty price. Working beneath Damo were Yotsuyu Yagiyama, Aisho Dainenjiyama, and the A. Phex Brothers. Jobin Higashikata served as a business partner of the organization, using his family's business to cover up the Locacaca trade. Aside from Jobin, all of the cartel members were killed by Josuke Higashikata and his allies.
The researchers of the Locacaca fruit are comprised of several Rock Humans working as doctors at TG University Hospital, including the mastermind Satoru Akefu. They wish to secure the New Locacaca for the benefit of the Rock Human race. Though the specific details of their goals are currently unknown, Urban Guerrilla believes that it could be used to bring about a massive change that favors Rock Humans over humanity, stating that it will "bring a whole new world to [them]".
- Much like Rock Humans, Araki is also allergic to mangoes, as noted in his author's note in Weekly Shonen Jump Issue #24, 2004.
- In the Love Love Deluxe arc, the rock human growth cycle was described differently. They didn't grow abruptly inside wasp hives, but instead would "molt" their whole bodies at once every six years. This transformation occurred during their sleep, and for some unknown reason, the pose they'd make when asleep would change each time.