The equation 4HgS -> 2Hg2S2 + 2S + O2

1. The chemical equation above represents the chemical reaction between Mercury sulfide (HgS), a substance commonly found in the mineral cinnabar, to produce Mercury (II) disulfide (Hg₂S₂), sulfur (S), and Oxygen (O₂).

2. Reaction conditions: For the reaction to take place, the temperature must be raised high enough. Usually, this reaction occurs at temperatures around 600 – 700 degrees Celsius.

3. Reaction process: When the temperature is high enough, Mercury sulfide will decompose into Mercury (II) disulfide, sulfur, and Oxygen.

4. Phenomena occurred: The reaction will produce a yellow gas (sulfur) and a colorless gas (Oxygen) rising from the initial solid (Mercury sulfide). Mercury (II) disulfide will remain as the solid residue.

Note: The above chemical equation may not be accurate as no reliable source of information can be found. HgS generally does not decompose to produce Hg₂S₂, S, and O₂. Instead, it is usually heated with O₂ to produce Hg and SO₂.