AboutA Wolf Clan Shalery is a combination of quarry and forge, where clansmen are fitted with shale armor. Shale has long been a common material in Wolf architecture, armor, and weapons, and one of the few blessings of their enslavement under the Lotus was access to this material, and the discovery that it affords some protection from Lotus magics.
The Wolf Clan's approach to bodily protection is typical of their approach to everything. Oversized plates of shale are hewn from the cliff face, shattered, then strapped to any body part they seem appropriate for. Wolf Clansmen don't mind the rough feel of it, let alone the weight, and if they did would rather die than admit it. Any discomfort merely makes up for the slight shame of asking for protection from enemy weaponry.
In Battle Realms and Winter of the Wolf, the Shalery functions as one of the Wolf Clan's sources of Battlegear; almost all Wolf units can go to the Shalery and receive Shale Armor Battlegear; these protective plates will reduce all damages suffered by Wolf units. A Shale Armored Wolf unit shall only suffer 75% damage from cutting, piercing, fire, blunt, and explosive attacks and 50% damage from magical attacks than s/he normally does.
Shale Armor stacks multiplicatively with a Wolf unit's natural resistances.
In real life, shale is a kind of sedimentary mud-rock consisting of fine grains of clay minerals, quartz, calcite, etc. Also, shale is found not deep underground, but in open areas (e.g. sedimentary basins) where slow-moving water may deposit sediments to be compacted into shale .
About hardness, shale is soft and fragile, so can be easily cloven along into thin sheets with metal knives or broken with hammer & pickaxe, so it's doubtful that real-life shale armor would be effective.
On the other hand, Battle Realms' story-writers might've confused shale with slate. While used interchangeably with shale & schist until the 20th century, slate is simply shale which has been buried underground for very long and metamorphized by heat & pressure, resulting in slate's greater hardness.