Citrine brooch

This exquisite brooch has a centre piece of a stunning & rare citrine stone, in an ornate setting of 18 carat gold. The date is 1920 and it comes complete with a safety chain. There is no modern hallmark stamp present - but there are some manufacturer markings typical of a gold piece from over 50 years ago. Since then all gold pieces produced must be stamped with a hallmark by the manufacturer. The lack of hallmark on this brooch shows its rarity and age. The markings are not completely clear but seem to read: 
N/S m|x - 1000
Measurements:
Height: 5.5cm
Width: 4cm
Depth: 1.5cm