There are a number of Resources to be found in Eiyuden Chronicle: Rising. Some of these Resources are obtained from various sources in the environment. This page will detail the location of the Emerald resource.
The Emerald is one of the gemstone resources, which you might find a few in chests throughout the game’s world. However, there are some spots where you can find the gemstones naturally, with the Emerald being a case. Unfortunately, there is only a single spot in the game where you can harvest the Emerald repeatedly. It will be in one of the deeper sections of the dungeon, so you might need to continue the main story until then. Once you have access to that section, head to the Runebarrows and fast travel to the Grand Hall signpost.
Upon arriving, head to the right and look for the passage that heads into the background. Note that if you don’t have access to this yet, continue with the story until you do. When you do, keep going right and ignore the upper path in this large room. Instead, you will basically want to go straight across from where you entered the room. If you see the Green Elementum Pillar, then you are underneath the exit and need to go up a little bit. In the final room here, fight the enemies, then start climbing towards the top of the room. On a smaller ledge, you should see a large crystal, which will be the Emerald.
Trading for an Emerald
Once you have leveled the Trading Post on Second Street enough, you will also be able to trade for an Emerald. In order to do so, you will need two items, an Ancient Crystal and a Lapis Lazuli. The Lapis Lazuli is another gemstone, but has three set locations in which to farm it on Snowpeak. As for the Ancient Crystal, it is the rare drop from enemies in the Runebarrows. So, if you are having trouble getting them, throw on some Rarity Pendants to increase the chance for them to drop.