Retrograde Blueschist – Location 30


 
Sample : Photo location 30
  Rock name : Retrograde Blueschist (Turner, 1982)

 

Megascopic description:

Bluish color with cement of whithish minerals and garnet.

Microscopic description:

The thin section shows the pseudomorphosed of glaucophane and/or garnet mineral into chlorite (retrograde metamorphism) but they still show the heteroblastic texture, locally the porphyroblastic texture with the garnet as porpyroblasts, anhedral in shape, 1.0 – 2.8 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 porpyroblasts garnet are usually rimmed by chlorite and the inclusions of quartz in the porpyroblasts garnet present to form poikiloblastic texture.

MACRO PHOTOGRAPH

MICRO PHOTOGRAPH

Sample: Photo location 30

PPL

XPL

The thin section of blueschist shows the porphyroblastic texture that the garnet as porpyroblast is rimmed by chlorite, 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 30

PPL

XPL

The thin section of retrograde blueschist that their groundmass shows the heteroblastic texture, consist of glaucophane (retrograde into chlorite), muscovite, quartz, and sphene, fine to medium in crystals size. The orientation glaucophane/chlorite and muscovite usually present to form the schistosity structure.

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