I believe the winner is a 1.5mm
diameter coin described by Brickstock (1987, page 93) as found in "Room 7" at Canterbury. It weighed under 0.02 grams.
The reason it was identified as a coin, and in fact as a
Fel Temp Reparatio Falling Horseman imitation, is simply the fact that it was found in a
hoard of 154 other FTR imitation coins ranging from 14mm down to 2.5 mm.
And your coin is most probably a
SALVS REIPVBLICE of
Theodosius II. I think I can see the full four letters (SIVS) before PF
AVG on the right -
Arcadius,
Honorius and
Johannes would have different
legend layouts.
Shawn