A special stone originally found in the Sinnoh region that can make certain species of Pokémon evolve. It is very tough and has a beautiful sheen.
Special evolution items like the Sinnoh Stone first arrived back with the second generation of Pokémon, and are now required when evolving Pokémon such as Roserade and Togekiss and Mismagius and Lickilicky and Yanmega and Froslass and Gallade and Gallade and Rhyperior and Rhyperior and Electivire and Electivire and Magmortar and Magmortar and Honchkrow and Honchkrow and Weavile and Weavile and Porygon-Z and Porygon-Z and Dusknoir and Dusknoir and Mismagius and Gliscor and Gliscor and Ambipom and Ambipom. When evolving these Pokémon, this item is required in addition to the candy, and is consumed when used.
How to evolve Roselia into Roserade
In order to evolve your Roselia into Roserade, you will need to have a Sinnoh Stone with you in your bags. You will also need to have all 100 candy, in the same way as with a normal evolution.
On your Roselia pokémon's screen, select the evolution through the usual in-game menu. The Sinnoh Stone and candy will be consumed, and you'll have a new Roserade with hopefully all the right moves.
In Pokémon GO, evolving Roselia into Roserade is a lot simpler than some of the other Pokémon games which required your Pokémon to also be traded to another player for the evolution to take place.
How to evolve Togetic into Togekiss
Evolving your Togetic into Togekiss works in the same way as with the other evolution above:
To evolve your Togetic into Togekiss, you will need to have a Sinnoh Stone with you in your bags. You will also need to have all 100 candy, in the same way as with a normal evolution.
On your Togetic pokémon's screen, select the evolution through the usual in-game menu. The Sinnoh Stone and candy will be consumed, and you'll have a new Togekiss.
How to evolve Misdreavus into Mismagius
Evolving your Misdreavus into Mismagius works in the same way as with the other evolution above:
To evolve your Misdreavus into Mismagius, you will need to have a Sinnoh Stone with you in your bags. You will also need to have all 100 candy, in the same way as with a normal evolution.
On your Misdreavus pokémon's screen, select the evolution through the usual in-game menu. The Sinnoh Stone and candy will be consumed, and you'll have a new Mismagius.
How to evolve Lickitung into Lickilicky
Evolving your Lickitung into Lickilicky works in the same way as with the other evolution above:
To evolve your Lickitung into Lickilicky, you will need to have a Sinnoh Stone with you in your bags. You will also need to have all 100 candy, in the same way as with a normal evolution.
On your Lickitung pokémon's screen, select the evolution through the usual in-game menu. The Sinnoh Stone and candy will be consumed, and you'll have a new Lickilicky.
How to evolve Yanma into Yanmega
Evolving your Yanma into Yanmega works in the same way as with the other evolution above:
To evolve your Yanma into Yanmega, you will need to have a Sinnoh Stone with you in your bags. You will also need to have all 100 candy, in the same way as with a normal evolution.
On your Yanma pokémon's screen, select the evolution through the usual in-game menu. The Sinnoh Stone and candy will be consumed, and you'll have a new Yanmega.
How to evolve Snorunt into Froslass
Evolving your Snorunt into Froslass works in the same way as with the other evolution above:
To evolve your Snorunt into Froslass, you will need to have a Sinnoh Stone with you in your bags. You will also need to have all 100 candy, in the same way as with a normal evolution.
On your Snorunt pokémon's screen, select the evolution through the usual in-game menu. The Sinnoh Stone and candy will be consumed, and you'll have a new Froslass.
How to get the Sinnoh Stone
The Sinnoh Stone is obtained from spinning Pokestops and Gyms. There is a very low drop chance of around 1% per spin to receive a Sinnoh Stone 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 Sinnoh Stone 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: