Glaucophane Thin Section

The contiguous outcrops of metabasalts fine grained amphibolite also contain small amounts of glaucophane and piedmontite.

Glaucophane thin section. Glaucophane in turkish blueschist glaucophane in greek blueschist the two samples on the left fine grained blueschist medium grained blueschist garnet studded retrograde blueschist after eclogite. For many years holmquistite was mistaken for glaucophane as the two look identical in thin section. Glaucophane in thin section.

Glaucophane has length slow riebeckite length fast. Darkest when c axis parallel to vibration direction of lower polarizer blue tourmaline is darkest w c axis perpendicular to vibration direction of polarizer. Glaucophane is also found in eclogites that have undergone retrograde metamorphism.

There is also a rare amphibole called holmquistite chemical formula li 2 mg 3 al 2 si 8 o 22 oh 2 which occurs only in lithium rich continental rocks. Under ppl the moderate to high birefringence is masked by the body colour. There is no twinning in glaucophane.

Blueschist ˈbluːʃɪst also called glaucophane schist is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures 200 to 500 degrees celsius approximately corresponding to a depth of 15 to 30 kilometers. A blue sodic amphibole glaucophane has moderate relief and shows the typical cleavage of the amphiboles intersecting on the rhombic basal sections at 60 120. Blue pleochroism in thin section grain mount distinguishes from other amphiboles.

This must be the most attractive malaysian rock in thin section because of the blue violet pleochroism of glaucophane and the yellow pink pleochroism of piedmontite set in a mosaic of normal quartz.