Polarized Light Microscopy
1). Plagioclase feldspars are commonly twinned. It is almost a rule. This photo has been taken from a sample of diorite from Adamello (Italy). This rock formed approximately 35 million years ago.
2). Myrmekite - a fine-grained intergrowth of plagioclase and quartz - in a high-grade metamorphic rock from the Ivrea Zone, Italy. Quartz forms the worm-like thin parts within larger plagioclase single crystals.
3). “Ocean Jasper”. This was a pendant carved out of “Ocean jasper” from Madagascar. After cutting it and putting it under a polarized-light ZEISS Axio Scope, it turned out to contain a microscopic garden of “orbicules” in a fine-grained silica matrix. The formation of orbicules or “spherulites” results from the process of devitrification of a rhyolitic lava upon cooling.
4). Graphite and feldspars in a ultra-high temperature granulite from the Kerala Khondalite Belt (India).
5). A blueschist from Aosta Valley, Italy. The rock is made of glaucophane, epidote, phengte.
6). Radiating andalusite crystals in a partially melted xenolith in rhyolitic lavas from Lipari, Italy. Taken with a digital camera mounted on a ZEISS Axio Scope, with crossed polarizers and the red tint plate (rotated as to reach the preferred colors).
Credit: Bernardo Cesare, Dipartimento di Geoscienze, Universita’ di Padova.