Coltan (short for columbite–tantalites and known industrially as
tantalite) is a dull black metallic ore from which the elements
niobium and tantalum are extracted.
Tantalum is used in the manufacturing of mobile phones,
personal computers, automotive electronics, and cameras.
Coltan mining is widespread in the DRC (Democratic Republic
of Congo).

Mai-Mai or Mayi-Mayi refers to any kind of community-based
militia group active in the DRC that is formed to defend local
communities and territory against other armed groups.
Most were formed to resist the invasion of Rwandan forces and
Rwanda-affiliated Congolese rebel groups, but some may have
formed to exploit the war to their own advantage by looting,
cattle rustling or banditry.

The name comes from the Swahili word for water, "maji".