almandinepyrope

Almandinepyrope, or almandine–pyrope garnet, refers to the garnet mineral that forms a continuous solid-solution series between the end-members almandine and pyrope. In this axis, iron (Fe) and magnesium (Mg) substitute for one another on the X site, while aluminum (Al) occupies the Y site, yielding the generic formula (Mg,Fe)3Al2Si3O12 across the series. The term describes garnets with intermediate compositions rather than a single fixed formula.

Geological occurrence and formation condition: Almandine–pyrope garnets are common in metamorphic rocks formed under high-grade conditions, such as pelitic, granulitic, and high-temperature/high-pressure environments. They also occur in some igneous and ultramafic rocks where appropriate chemical conditions permit garnet crystallization. The composition along the pyrope–almandine axis can provide information about the metamorphic history and pressure–temperature path of the rock.

Physical properties: Garnets in this series crystallize in the isometric (cubic) system and commonly form: reddish to purplish-red crystals, often displayed as dodecahedra or trapezohedra. They are individually relatively hard, with no true cleavage, and have a typical specific gravity in the mid-range for garnets. Gem-quality examples are commonly used as gemstones, valued for their color and brilliance.

Related varieties: When garnets in this series display specific color ranges, they may be described as rhodolite if the intermediate pyrope–almandine composition yields pink to purplish-red tones. Almandine–pyrope garnets contribute to the broader garnet family found in metamorphic petrology and gemology.