The Onverwacht Group or Onverwacht Series is a series of greenstone belts and volcanic rock formations from the Archean Eon in the Kaapvaal Craton in South Africa and Eswatini.

A well known part of the Onverwacht Series is visible in the Komati valley, located in the east of the Transvaal region.

The Onverwacht Group can be divided into two subgroups with six formations:

• Geluk Subgroup
  • Swartkoppie Formation – 920 metres (3,020 ft)
  • Kromberg Formation – 1,920 metres (6,300 ft)
  • Hooggenoeg Formation – 4,850 metres (15,910 ft)
• Tjakastad Subgroup
  • Komatii Formation – 3,500 metres (11,500 ft)
  • Theespruit Formation – 1,980 metres (6,500 ft)
  • Sandspruit Formation – 3,200 metres (10,500 ft)

The fossils found in the Onverwacht Series are among the oldest found on Earth.

• Archean life in the Barberton Greenstone Belt
• Warrawoona Group

• Engel, A.E.; Nagy, B.; Nagy, L.A.; Engel, C.G.; Kremp, G.O.; Drew, C.M. (1968). "Alga-Like Forms in Onverwacht Series, South Africa: Oldest Recognized Lifelike Forms on Earth". Science. 161 (3845): 1005–1008. doi:10.1126/science.161.3845.1005. PMID 17812798. S2CID 30694721. Retrieved 12 July 2008.

• (in German) Der Barberton Greenstone Belt und Komatiite