Moonstone is an ivory colored metal found in veins throughout Tamriel. They are generally used, sometimes in tandem with quicksilver to make elven armor, which was a closely-guarded secret for the longest time, to the Altmer of Summerset. But it is also the signature material used in Khajiiti-styled armor. Moonstone melts at a much higher heat than quicksilver, making it tricky to work with both of them together. Saltwater is required to quench the hot metal when making elven armor.
In the province of Cyrodiil, Elven Armor is considered some of the strongest light armor, better than mithril but weaker than glass. It was on par with ebony heavy armor. In Skyrim, normal elven armor is stronger than chitin and leather armor, but weaker than scaled armor. All the while, gilded elven armor is stronger than scaled and normal elven armor, but it is inferior to light stalhrim and glass. Refined Moonstone is used to create the armor used by the Golden Saints of the Shivering Isles, with gold and a daedra's heart.
For the longest time, moonstone is used in various Khajiit styled constructs, namely weapons, armors, furnishings, and various other items. For example, wooden furniture such as tables and beds are made with moonstone, alongside heartwood and regulus. Metal braziers and torches are primarily used with the latter. Tailors make Khajiit fabric with a myriad of materials, it mostly uses bast, among other materials and occasionally citrine. Various types of Khajiiti bottles and containers are made from moonstone, coincided with materials like Bervez Juice and Frost Mirriam. Small warrior figurines carved from moonstone are placed in superstitious people's cabinets, to ward off thieves.
In 2E 582, a chunk of rock known as the holy moonstone was in circulation throughout Tamriel. According to local legend, it fell from the moons (Masser and Secunda) centuries prior, but no one was able to confirm this. It is unknown if it is related to the common moonstone. The ancient secret of Moonstone's use in elven armor was revealed to the world in the seventh century of the Second Era. When the Dunmeri slave, Ulvul Llaren escaped the clutches of the master smith, Nuulion, he unleashed the secrets to crafting elven armor out of complete spite. The tale has since been dubbed the "Betrayal of Ulvul Llaren".
In Skyrim, moonstone veins are found across the mountains. Some of the largest veins of moonstone is found in the ruined city-state of Mzulft and the moonstone mines of Soljund's Sinkhole, which is located near the eastern base of Karthspire and the Karth River. It is extremely rare on the island, Solstheim, with only one vein found at the Altar of Thrond.