Antimony variants......there are hundreds of different chemical strains, and also many colors of antimony and it's associated compounds. Both red and black antimony are very common, and used in industry for a variety of purposes. In fireworks displays that I used to put on for municipalities, I used them both often to create different colorings in sprays and fountains. Over time, Azteca has most likely hit a number of different antimony variations, differing in purity and chemical makeup, which would change it's coloration from sample to sample...as antimony is rarely discovered in it's pure state. Only the chemical assays of the core samples can indicate the true substrate and the content therein, not necessarily the color...hope that helps.