Zelda Breath of the Wild – How to Deal with Yiga Clan Guards in Breath of the Wild

Gems seem to serve three primary purposes:

• Being worth a boatload of money.
• Being used as an upgrade component.
• Being able to made into accessories.

Some items, like the Berserker set, require 2 diamonds to upgrade. There are likely other sets like this, but I'm uncertain.

As Sam mentioned, you can also use gems to get circlets and earrings from the Gerudo Jeweler. They take up a head slot (so they're not particularly useful in most cases) and there are 6 total:

• Amber (8 amber = +4 def earrings)
• Opal (8 opals = swim speed boost earrings)
• Ruby (5 rubies = ice resist up circlet)
• Sapphire (5 sapphires = fire resist up circlet)
• Diamond (3 diamonds = guardian resist circlet)
• Topaz (5 topaz = electric resist earrings)

This is of course only doable after you give her the 10 Flint.

ChuChu Jelly (the blue kind) can be 'empowered' into the various colors of elemental ChuChu jelly by exposing it to that element. (I.e. For red jelly, put it in a fire, for white jelly, put it down in a cold snowy area, etc.)

Elemental ChuChu jelly, like the ChuChu's themselves, explodes when impacted in an elemental burst. Icy jelly will freeze enemy, red jelly will start fires and detonate explosives, etc. you can abuse this by, for example, placing a jelly on the ground and firing an arrow at it to detonate it.

In addition, the elemental ChuChu Jellies are more valuable. Potions made with them rather than regular jelly will be more valuable. The easiest way to use it is to drop a large amount of regular jelly on or near a fire, then make potions using several of the Red ChuChu jelly.