marcelite

Marcelite is a mineral belonging to the garnet group, specifically a member of the pyralspite series. Its chemical formula is typically represented as (Ca,Fe2+)3(Al,Fe3+)2(SiO4)3. It is characterized by a specific range of chemical compositions, where calcium and iron(II) can substitute for each other, and aluminum and iron(III) can also substitute. This solid solution series means that pure marcelite is rare, and most specimens exhibit intermediate compositions with other garnets like andradite or grossular.

Marcelite is known for its distinctive color, which can range from reddish-brown to yellowish-brown. The presence of iron ions in its crystal structure contributes to its coloration. It crystallizes in the isometric crystal system, forming dodecahedral or trapezohedral crystals. Marcelite is found in metamorphic rocks, particularly those that have undergone contact or regional metamorphism. Its occurrence is often associated with silicate-rich environments where the necessary elements are available for its formation.

While not as common as some other garnet varieties, marcelite has been identified in various geological settings worldwide. Its identification and classification are based on its optical properties, chemical composition determined through X-ray diffraction and electron microprobe analysis, and its crystal structure. It is considered a relatively stable mineral under certain metamorphic conditions.