Symplectites

Symplectite: A general textural term that refers to fine-grained vermicular intergrowth of minerals, which may or may not show radial structure like kelyphites. Symplectites may be a breakdown product of primary phases such as garnet, aluminous pyroxene or some other phases; or a reaction product between two incompatible phases such as olivine and plagioclase at high pressures.

Omphacite replacement by symplectites is common structure in eclogites and was described in detail by Briere (1920) and Eskola (1921). These authors painstakingly identified the clinopyroxene + plagioclase and amphibole + plagioclase associations among the cryptocrystalline products that replace the omphacite. This process of omphacite replacement was apparently first understood by the Italian petrologist Franchi (1902a) and afterwards by Eskola (1921). It was interpreted as resulting from the exsolution of the jadeite molecule from omphacite, which results in albite production:

omphacite [Jadeite-Augite solid solution] + quartz = albite + augite

Bibliography

• Godard, G. (2001). Eclogites and their geodynamic interpretation: a history. Journal of Geodynamics, 32(1-2), 165-203.
• Godard, G., & Martin, S. (2000). Petrogenesis of kelyphites in garnet peridotites: a case study from the Ulten zone, Italian Alps. Journal of Geodynamics, 30(1-2), 117-145.
• Obata, M. (2011). Kelyphite and symplectite: textural and mineralogical diversities and universality, and a new dynamic view of their structural formation. New frontiers in tectonic research-general problems, sedimentary basins and island arcs. InTech, 93-122.
• Obata, M., & Ozawa, K. (2011). Topotaxic relationships between spinel and pyroxene in kelyphite after garnet in mantle-derived peridotites and their implications to reaction mechanism and kinetics. Mineralogy and Petrology, 101(3-4), 217-224.

Photo
Garnet crystals with plagioclase + spinel + amphibole corona, amphibole (brown-green) and omphacite (symplectitic mixture of diopside and albite). PPL image, 1x (Field of view = 9mm)	Garnet crystals with plagioclase + spinel + amphibole corona, amphibole (brown-green) and omphacite (symplectitic mixture of diopside and albite). PPL image, 1x (Field of view = 9mm)	Garnet crystals with plagioclase + spinel + amphibole corona, amphibole and omphacite (symplectitic mixture of diopside and albite). XPL image, 1x (Field of view = 9mm)
Garnet crystals with plagioclase + spinel + amphibole corona, amphibole (brown-green) and omphacite (symplectitic mixture of diopside and albite). PPL image, 1x (Field of view = 9mm)	Garnet crystals with plagioclase + spinel + amphibole corona, amphibole (brown-green) and omphacite (symplectitic mixture of diopside and albite). PPL image, 1x (Field of view = 9mm)	Garnet crystals with plagioclase + spinel + amphibole corona, amphibole (brown-green) and omphacite (symplectitic mixture of diopside and albite). PPL image, 1x (Field of view = 9mm)
Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. PPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)
Omphacite → kelyphitic mixture of diposide and albite. PPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)
Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. PPL image, 10x (Field of view = 2mm)
Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. PPL image, 10x (Field of view = 2mm)	Omphacite → kelyphitic mixture of diposide and albite. XPL image, 10x (Field of view = 2mm)