Currency
10 copper pieces = 1 silver piece
10 silver pieces = 1 gold piece
While gold and silver have remained stable through the Great War, copper has become a bit of an issue. Its alloys are highly valuable for the war effort; not as weapons of course, but as tools and fixtures. Most "copper pieces" are actually made of nickel nowadays.
Stonework
The three major stones on Ozel tend to be Limestone, Marble, and Granite. The durability of granite has enabled much of the infrastructure in the Three Kingdoms to survive; in fact, roughly 40% of architecture was laid during the Territorial Era. Marble, meanwhile, can be found in most Dion buildings and statues. The varying patterns of the stone prompted many architectural works based on aesthetics, leading to many construction techniques to have come from Dion. Limestone, on the other hand, was found mostly in Sadah. The durability combined with smoothing methods allowed towering structures that lasted a long time in the generally arid environment of the nation. It also provided a good base for the vibrant paints Sadah used in their artwork, owing to the diverse amount of herbs in its vital riverbeds.
Metals
While steel has been known for some time, iron was mostly used for tools and other mechanisms. With the exception of Sadah and Adraria, plentiful ore could be found all around the continent. Where iron was lacking, however, mithral could likely be found. Iron and steel proved durable enough to withstand blows and cuts, but mithral has been widely sought after as a magically resistant metal. Known also as Blue Counterspell, the metal has been vital in numerous major battles, as it effectively nullified magic brigades. On the opposite end of the spectrum, Adamantine is an extremely rare mineral that, when combined with iron, creates a material that, while not very durable, is able to shear through steel like butter.
Once thought to be impossible, or not practical, the Empire was able to reliably manufacture a compound known as Mithsteel. Using the same principles behind making steel (that is, purifying iron by adding Carbon), the Empire was able to combine Mithral with some unknown substance. Mithsteel is extremely durable, both magically and physically. Most importantly, however, was its pliability, allowing it to be formed into armor of varying shapes while still being relatively lightweight. This has been mass-produced into various armored carts, towers, and even infantry armor for key military leaders.