Pierre Sinnoh - Evolution Item
Une pierre spéciale originaire de la région de Sinnoh, qui peut faire évoluer certaines espèces de Pokémon. Elle est très solide et a un superbe éclat.
Special evolution items like the Pierre Sinnoh first arrived back with the second generation of Pokémon, and are now required when evolving Pokémon such as Coudlangue and Rhinastoc and Bouldeneu and Élekable and Maganon and Togekiss and Capidextre and Yanmega and Corboss and Magirêve and Scorvol and Dimoret and Mammochon and Porygon-Z and Gallame and Roserade and Noctunoir and Momartik. When evolving these Pokémon, this item is required in addition to the candy, and is consumed when used.
How to get the Pierre Sinnoh

The Pierre Sinnoh is obtained from spinning Pokestops and Gyms. There is a very low drop chance of around 1% per spin to receive a Pierre Sinnoh or any of the other evolution item, and there is an equal chance of obtaining each of the 5 currently available items.
There's no way to ensure that the Pierre Sinnoh will drop, but with only 4 other items, there's a greater than 50% chance that you'll receive one once you've spun over 250 Pokéstops.
The 7th day streak bonus gives you a very high chance of obtaining one of the evolution item, but it's not believed to be guaranteed.
Other evolution items
The other evolution items that can be found in Pokemon GO are: