The Hemitetartemorion denomination
The hemitetartemorion is a tiny Greek denomination worth half a tetartemorion - equivalent to 1/8th of an obol.

It weighs 0.09 grammes, and usually measures 3-5mm in diameter.

It was the smallest Greek denomination, and was equivalent to 1/48th of a days wage. It was very infrequently struck.
Hemitetartemorion

(1) Erythrai 520-480 BC
Obverse: Rosette or floral pattern with central pellet
Reverse: Five pellets within cruciform incuse
Ref: SNG Kayhan 740 (Erythrai?); SNG von...
(2) Miletos | Erythrai c. 520-480 BC
Obverse: rosette with central pellet
Reverse: incuse quadrilobe, Stellate pattern of five pellets
Ref: SNG Kayhan 740; Klein 433.