925 Sterling Silver:
925 Sterling Silver is a combination of 92.5% pure silver and 7.5% of another metal, and it is the highest percentage of fine silver possible for jewelry subject to everyday wear. Fine silver (99.9% pure) is generally too soft and malleable for jewelry. Therefore, it is usually combined with copper to give it strength, while at the same time preserving both the ductility and beauty of its original form.
Marcasite The mineral marcasite, sometimes called white iron pyrite, is iron sulfide (FeS2) with orthorhombic crystal structure. On fresh surfaces it is pale yellow to almost white and has a bright metallic luster. It tarnishes to a yellowish or brownish color and gives a black streak. It is a brittle material that cannot be scratched with a knife. It typically forms under low-temperature highly acidic conditions.