Sky Gemstone is one of the rare treasure in Final Fantasy XV and is required to upgrade the Circular Saw by talking to Cid at Hammerhead Outpost and accepting the Better Circular Saw quest. Unlike some other treasures, it can be sold for a very high price but given the rarity, players should hold on to it in case they need to upgrade their Circular Saw.
Final Fantasy XV Sky Gemstones Locations
Currently, there is only one known way to acquire a Sky Gemstone and that is through a quest chain at Galdin Quay. While on the way to the restaurant at the center of the area, players will encounter a hungry cat which begins the Kitty Catering quest.
The cat needs a special type of fish, Trevally, which can be fished from a nearby spot. However, the fish is only available during the day so players need to keep that in mind before they go out and starting fishing.
Once the correct fish has been caught, players need to return to the restaurant and have the chef in the middle of the restaurant cook it before it can be fed to the cat.
Completing this quest however will not reward the players with the Sky Gemstone as they will need to encounter the same cat once again, this time at Cape Caem lighthouse. This area is accessible after players have received the Brave New World main story quest.
Talking to the cat at the Cape Caem lighthouse will start the Feline Feast quest where players will have to find some more food for the cat. A vendor at the Cape Caem outpost sells for luxury cat food for 20,000 Gil. After feeding the cat, she will reward players with a Sky Gemstone.
The Sky Gemstone can be brought to Cid to complete the Better Circular Saw quest although the upgrade takes a couple of days so plays can head out and do other quests while the upgrade is being done.