Collecting is not a skill per se, and does not have the associated 1-10 levels of normal skills.
Gems can be found lying around (through the Collection Helper), by Rummaging in a trash can (only avaliable to some Sims), or by Exploring the Catacombs of the Mausoleum.
To get the rarest two gems, we recommend sending an unemployed Sim with a Moodlet Manager to Explore the Mausoleum (queue Explore, Cure self, Explore, Cure self, etc.). It could take days, but it’s less effort than checking if they’ve spawned.
As far as I can tell, the Collection Helper does not “identify collectables”.
New cuts are unlocked by sending gems to be cut.
For example, if your Sim has never sent a gem to be cut, only “Emerald Cut” will be available. If your Sim is a Gem Collector, only “Emerald Cut” and “Heart-Shaped Cut” will be avaliable. After four gems have been sent to be cut, “Oval Cut” will be unlocked, and so on.
Uncut gems look like rocks with the gem stone sticking out. If the gems have been saved to bin (either by being in the house, family inventory or a Sim’s inventory), they become a “chunk” of the gem.
|Rarity||Gem||Cut||Cost||Multiplier||Availability (Cumulative)||Availability (From Last New Cut)|
|Common||Blue Topaz||Emerald Cut||$10||×1.25||0||0|
|Common||Smoky Quartz||Oval Cut||$20||×1.5||4||4|
|Uncommon||Yellow Sapphire||Marquis Cut||$75||×2.25||30||14|
|Uncommon||Tanzanite||Crystal Ball Cut||$100||×2.5||45||15|
|Rare||Luminorious Gem||Heart-Shaped Cut||$1000||×5|
|Special||Rainbow Gem||The Heart-Shaped Cut is only available to a Sim that is a Gem Collector.|