These devices seem to have been created by Ovates during the time of the Great Rekindling in Æropa. A Historical Bard Song from Avillonia tells the tale of the invasion of a village by Viking Raiders, and how they defended themselves with acorns of Copper, Silver, and one of Gold.
Such devices are made by Æropean Priestcraefters or Wisepeople of Nature oriented deities, such as many of the Celtic ones, Greco-Roman ones such as Demeter, Diana, Silvanius, etc. They are usually given to acolytes to use as defensive tokens for temples, shrines, to laypeople for villages and hamlets, or those on quests who need them.
Such devices always look like an Acorn perfectly crafted in Copper, Silver, or Gold. They have no known runes on them, although after created they're usually kept in a box inlaid with runes/symbols of the creator's deity, until given to potential users. Heka-Detection on such devices, which aren't normally masked, will reveal an aura tuned to nature and elemental power.
All things being equal, Copper is the most common acorn, Silver being uncommon and Gold rare in cases where these are found, but is not always the case, especially where temples are concerned, as the nature of the deity may favor the acorn.
The raw metal value for these devices are equal to 1 coin weight.
Note: No other metals are known used these acorns. It is thought that Platinum and Oricalcium don't have as much a link to the natural elemental energies as the other metals, and it is known that such substances will only work with a "Pure" metal, so Electrum, Brass and Bronze would not work.
These Acorns are inactive until rubbed (which takes 1CT). Afterwards, they are "active". If an acorn of this nature is thrown, or used in a sling, when it hits the target, it will cause and explosion that will affect all within a 10' radius. The effect depends on the metal. The target must roll a D6 explosion multiplier, while all others must roll D3 explosion multiplier.
An activated acorn only stays active for 1BT, and if it is not used in time, the enchantment fades from the device, and such a device can't be recharged. (Note in other cases such a device is destroyed.) Thus, dropping an acorn will work if the device falls more than 10 feet, or is thrown hard but it won't go off if it's "fumbled" in combat.