Complex sentence: The true (neutral) copper (II) carbonate CuCO 3 is not known to occur naturally, is decomposed by water or moisture from the air, and has been synthesized only in 1973 by high temperature and very high pressures.
Split into simpler sentences: The true (neutral) copper (II) carbonate CuCO 3 is not known to occur naturally. It is decomposed by water or moisture from the air, and was synthesized only in 1973 by high temperature and very high pressures.