Retrograde Blueschist – Location 4

Sample : Photo location 4
Rock name : Retrograde Blueschist (Turner, 1982)

Megascopic description:

Strong foliation, cataclastic cemented by whitish minerals and garnet. Patches of light green mineral are found, looks like open space filling. Very fine fractures filled with pinkish-brownish minerals are common.

Microscopic description:

The thin section shows the intensive pseudomorphosed of glaucophane mineral into chlorite (retrograde metamorphism) but they still show the heteroblastic texture, locally the porphyroblastic texture with the garnet as porpyroblasts, anhedral to subhedral in shape, 0.7 – 1.8 mm in crystals size, in the fine to medium groundmass of glaucophane, muscovite, quartz, and sphene, less than 0.5 mm in crystals size. The orientation of nematoblastic and/or lepidoblastic minerals such as glaucophane (retrograde into chlorite) and muscovite usually present to form the schistosity structure. The inclusions of quartz in the porpyroblasts garnet present to form poikiloblastic texture.

 

MACRO PHOTOGRAPH

MICRO PHOTOGRAPH

Sample: Photo location 4

PPL

XPL

The thin section of blueschist shows the porphyroblastic texture with the garnet as porpyroblasts, in the groundmass of glaucophane, muscovite, quartz, and sphene, fine to medium in crystals size. The orientation glaucophane (retrograde into chlorite) and muscovite usually present to form the schistosity structure.

MICRO PHOTOGRAPH

Sample: Photo location 4

 

PPL

XPL

The thin section of blueschist shows the porphyroblastic texture with the garnet as porpyroblasts, in the groundmass of glaucophane, muscovite, quartz, and sphene, fine to medium in crystals size. The orientation glaucophane (retrograde into chlorite) and muscovite usually present to form the schistosity structure.

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