Hardness on Mohs-scale: 2,6 – 4,6
Specific gravity: 2,6 – 2,8
Streak: white
Chemical structure: CaCO3 : 87-90%, H2O: 2,5-3%
Conchiolin: 6-9%, Others: 1%
Natural pearls are usually measured in pearl grains:
1 grain = 0,05 gr = 0,25 ct
Japanese use their own system as follows:
1 Momme = 75 grain = 3,75 gr
1000 Momme = 1 Kan = 3,75 kg
The size of culture pearls are expressed in mm (diameter), their weight is expressed in gr, kg, ton, though at the pearl-auctions in Kobe also the Momme and Kan units are used.