A very nice, circular piece.
Obverse: eagle of the Empire of the 1832 pattern, between its legs and tail the initials НI, in a rope border, in the outer border an inscription beginning with a rosette:
ЧИСТAГО СЕРЕБРА 4 ЗОЛОТНИКА 21 ДОЛЯ;
Reverse: in a laurel and oak wreath crowned inscription:
РУБЛЬ/1877/СПБ;