What mineral is known for the process of isomorphous replacement in garnets?

The correct answer is rooted in the concept of isomorphous replacement, a key process in the formation of garnets. This process involves one mineral or ion substituting another in the crystal structure without disrupting the overall framework. Almandine, a type of garnet, serves as a classic example of this phenomenon.

Almandine is characterized by its composition, which typically includes iron (Fe) and aluminum (Al). These elements can undergo isomorphous replacement with other similar-sized ions such as magnesium (Mg), manganese (Mn), and calcium (Ca). This flexibility in its crystal structure allows for variations in the mineral’s composition, leading to the rich diversity seen within the garnet family.

In terms of garnets, other types such as grossular, pyrope, and spessartine also exhibit isomorphous replacement but in different contexts and combinations of elements. For instance, grossular primarily contains calcium and aluminum, while pyrope is rich in magnesium and aluminum. Each variety has its unique characteristics and chemical compositions, illustrating the broader concept of isomorphous replacement but within a more specific range than that found in almandine. This foundational understanding of how almandine's structure allows for isomorphous replacement