There are 5 types of Gnome Runes:
-Gray (Argo & Yaz)
-Green (Ezav & Khagann)
-Blue (Rayno & Terp)
-Purple (Fey & Frey)
-Red (Bego & Anguz)
They are used to obtain many precious resources and items, but also gnome coins, both regular and valuable.
To open a rune you need to charge it with quicksilver (different colored runes require different amounts of quicksilver to charge). To activate charged rune, in order to get runic casket and get the goodies, you'll need to be on a specific location for each rune, and, in all cases but with gray runes, fight off treasure guardians (the better the rune the stronger the guardians).