Very well crystallized, lustrous, rich native silver, combined with acanthite. 

Although there is no silver mining today, Kongsberg is very well known for its silver mining.

Although there is no silver mining today, Kongsberg is very well known for its silver mining.

The silver mines in Kongsberg were in operation from 1623 until 1958. Total production exceeded 1,3 million kg of silver. In fact, the name "Kongsberg" is translated to "The king's mountain". At the most (in 1770) over 4000 people worked here, and the mines accounted for about 10% of the gross national product of the Danish–Norwegian union in its 335 years of history.

So this piece is also a part of history. I don't know when it was found.