Two diamond shaped objects observed in sky.

Note:  The date and time of observation is not exact.  It was during the summer of 1980 or 1981 in the afternoon.  Objects observed during a weekday, as my parents were at work.
 My brother and I were in the back yard swimming.  A couple of shimmering objects caught our attention in the north sky.  The objects were too far away to determine what they were, so I went in to get a pair of binoculars.  When observed through the binoculars, they were 2 diamond shaped objects spinning.  (from our point of view, they looked like mirrors rotating left to right).
 I thought that they might be part of a weather balloon, but no other objects were in the sky, no balloon, attached wires, etc.
 My brother and I went to get on top of the garage for a better view. By the time we got on the garage the objects were gone.
 The St. Louis airport was near our home and I do not recall any unusual air traffic in the vicinity.
Witness indicates that date of sighting is approximate.  PD