Rock Human

"His skin is rock! He's a living human with rock skin!"

- Josuke Higashikata about Yotsuyu Yagiyama, JJL Chapter 30

The Rock Humans (岩人間) are a race of mysterious beings that serve as the primary antagonistic force in JoJolion.

Summary
Rock Human is the term used to describe creatures that evolved with Silicon as the element they are primarily composed of. While in their original form, most biological activities come to a halt and they're able to endure high and low temperatures, dryness and other factors in nature.

One of the defining characteristics of a Rock Human is that they are silicon-based organisms unlike humans who are carbon-based organisms.

While they are generally represented as humans, Rock Animals (岩動物) also exist. Iwasuke, a dog of unknown origin, appears to have similar abilities and is described as a Rock Dog, whereas Doremifasolati Do is described as a pet Rock Animal.

Origin
The Rokakaka Fruit, and subsequently Rock Humans, likely have their origin in the island of New Guinea, with several of the inhabitants who had consumed the fruit becoming Rock Humans. During World War II both Australian and Japanese forces fought in New Guinea, which allowed them to come in contact with the fruit, and whilst Japanese Rock Humans have been present in the series, it is unknown if any Australian Rock Humans exist.

Hibernation
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.

Biology
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.

Rock Humans do not grow gradually, but "molt" their whole bodies at once every 6 years. This transformation occurs during their sleep, and for some unknown reason, the pose they make when asleep will change each time. 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.

Behavior
Rock Humans eat plants, fruits, nuts, meat, fish, and all other forms of life. They enjoy honey, and all are allergic to mangoes.

They hold a certain reverence for the power found within the Earth and nature. Because they are fundamentally able to live through weather changes, they require no assets such as a house or land.

However, they are unable to safely coexist or mutually understand human society. Because their natural environment is 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 Man 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 unknown.

Members
Although not much is known about the Rock Humans' society at large, it can be inferred that their typical behavior 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.

Rokakaka Organization
Led by, this group of Rock Humans prioritize gaining the power of the New Rokakaka's equivalent exchange, and to secretly obtain and sell Rokakaka fruits for wealth.

Smuggling Cartel
Within the organization is a small faction led by Tamaki Damo, dedicated to smuggling Rokakaka 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 Rokakaka trade. Aside from Jobin, all of the cartel members were killed by and his allies.

Researchers
The researchers of the Rokakaka fruit are comprised of four Rock Humans working as doctors at TG University Hospital, including the mastermind Satoru. They wish to secure the New Rokakaka 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]".

Trivia

 * The concept of the people turning into rock when hibernating is similar to the Pillar Men in Battle Tendency.
 * Although their motives are unclear, at this point in the manga the "Rock Humans" are the collective antagonists of JoJolion.
 * Spikes or bulbs (often similar to the ones of the Rokakaka fruit) are a recurring design element delegated to the Rock Humans and their associates.
 * Jobin is currently the only non-Rock Human in JoJolion to feature this design motif.