Gemstones are a relatively new way to boost your stats. While mining Gemstones can be a good money making method, this isn't what this guide is about. I'm gonna focus on what Gemstones are and what you should do with them.
The different Gemstones and their qualities (texture pack: Furfsky Reborn)
There are 8 types of Gemstones in the game, each associated with a stat, color and area in the Crystal Hollows (with the exception of Ruby Gems) which is where you will find them (Opal Gems are the only Gems found outside of the Crystal Hollows, on the Crimson Isles). These Gemstones are:
Amber Orange Goblin Burrows Mining Speed
Jade Green Mithril Deposits Mining Fortune
Topaz Yellow Magma Fields Pristine
Sapphire Blue Precursor Remnants Intelligence
Amethyst Purple Jungle Defense
Ruby Red Health
Jasper Pink Fairy Grotto Strength
Opal White Smoldering Tomb True Defense
Gemstones come in 5 different tiers:
Flawed (80 Rough)
Fine (80 Flawed = 6400 Rough)
Flawless (80 Fine = 512 000 Rough)
Perfect (5 Flawless = 2 560 000 Rough)
The main use of Gemstones, apart from being used in some recipes or forge recipes, is to apply them to your gear. That however can't be done with any item, the item has to offer a fitting Gemstone slot. To check if your item has a Gemstone slot (and to apply Gemstones to it) go to the Gemstone Grinder next to the entrance to the Crystal Hollows and put it in. Now it will either give you an error saying this item doesn't have any slots, or show you the slots underneath the item. Clicking on a fitting Gemstone will place that Gemstone into the Gemstone slot, removing it will cost a fee depending on the tier of the Gemstone. You can also view all the items that can have Gemstones applied by clicking Gemstone Guide in the Gemstone Grinder.
Now there are 2 details about slots. First of all, there's different kind of Gemstone slots. Only universal slots can hold any Gemstone, there's also slots that can only hold one specific kind of Gemstone (e.g. the Sapphire slot on the Aspect of the End) or can only hold a certain category of Gemstones. The categories are:
Offensive (Sapphire or Jasper)
Defensive (Ruby, Amethyst or Opal)
Combat (Offensive + Defensive)
The other detail is pretty important. Not all slots are unlocked by default. Some slots need to be unlocked first by paying a combination of Gemstones and coins. This can be really expensive, as even the Jasper slot on an early game weapon like the Aspect of the Dragons costs about 2m to unlock with the current prices, but will never cost less than 500k due to NPC sell prices. The price on Necron Armor or any of the other wither armor sets however is way more significant: Both slots cost more than 16m to unlock. PER PIECE.
How to Get Items with Good Gems on the Auction House
I think at this point you'll have realized that it's extremely important to see if an item you buy on the auction house has gems applied and if it has it's Gemstone slots unlocked.
Luckily both is shown in the item description. On an item with Gemstone slots you will see these brackets [ ] representing the Gemstone slots. Grey means the slot is empty while other colors represent the rarity of the gem that's in this slot. The icon inside of the brackets represents the type of the slot, but you can also see that in the Gemstone Grinder. Way more important than the icon itself is again the color, with grey meaning the slot is locked, white meaning it's unlocked but empty and every other color representing the type of Gemstone that's applied to the slot.
Please note that there are lots of items with unlocked slots in circulation, due to any item that was crafted/obtained before 14.09.2021 having it's Gemstone slots unlocked by default. Often times the price for those items will be the same or almost the same as for an item with locked slots. For that reasons you can save millions of coins by carefully looking at the Gemstone part of the item description.
Necron's Boots with locked slots
These boots have 2 Fine quality Gemstones applied to them (blue brackets), one of which being a Jasper (pink), the other a Sapphire (blue). The Gemstone stat boost is displayed by the pink numbers (excluding gear score ofc).
You will probably find cheaper Necron's Boots with Gemstones than these, they are not worth the price even if they are more worth it than the 12m ones.
Necron's Helmet with locked slots
Unlocked yet empty slots. Upgrading the left Helmet to this one would cost more than 30m atm.
Boosting Your Stats
It is very important to always have Gemstones applied to all available slots.
For everyone that just started playing I recommend Flawed gems, as they are extremely cheap and can give decent stats for that stage of the game.
In terms of cost effectiveness Fine is definetely the best.
Upgrading to Flawless Gems will not be worth it for a long time, except for Topaz Gems if you are Gemstone mining.
Most of the times offensive is better than defensive in Skyblock. That's why you should aim to put Jasper Gemstones on every weapon and every armor you use for combat.
Mage weapons only accept Sapphire gems so you don't really have a choice there.
For mining prioritize Topaz (only if you're Gemstone mining) over Jade over Amber
Examples on what to put Gemstones on
(ignoring locked slots)
Basically any of the boss chest dungeon armors/weapons accept gems.
Other important items to put gems on are:
Any Dragon armor
Any Mining armor
Higher tier drills
Aspect of the End
Aspect of the Dragons
Slayer swords (Reaper Falchion/Axe of the Shredded, Katanas (Eman), Daggers (Blaze))