This issue involves the relationship between the color of a substance and its chemical composition and structure. Firstly, we need to clarify that pyrite is not a standard chemical term, but may refer to a compound or mixture containing sulfur and iron, and the term ''yellow pyrite'' mentioned here may be a non-specific or colloquial term. However, when we talk about ferrous sulfide (FeS), we are discussing a specific compound with a definite chemical formula.
The color of ferrous sulfide is black, which is related to its specific crystal structure and electron arrangement. In ferrous sulfide, iron ions (Fe ² ⁺) and sulfur ions (S ² ⁻) are bound together through ionic bonds. This combination method results in a unique distribution and transition pattern of electrons in the crystal, which absorbs most of the visible light spectrum components and reflects mainly black or dark light.
On the other hand, if the term "yellow sulfur iron" refers to another compound containing sulfur iron, such as natural sulfur (pure sulfur, usually yellow) or a mixture of sulfur and iron (such as pyrite FeS ₂, which is golden yellow), then the color of these substances may be due to their different crystal structures, electron arrangements, or the presence of impurities.