10.14.11 - A really gneiss day (WARNING: Academic Content)

Monolithic stone temple

          We spent most of today temple touring in Mamalla Puram. It was amazing to witness the intricate structures and mind astounding to think about the degree of creativity and the amount of labor necessary to create them. The most impressive thing that I took away from visiting the temples was an insight on the construction process. Apparently, ancient Indians knew their geology. These ancient peoples utilized the folliation planes of the metamorphic rock (gneiss) by strategically chistleing square holes into the rock, hammering in small pegs of wood, and soaking the wood pegs in water. The expansion of the soaked wood resulted in a force that pried the rock cleanly apart along the folliation plane. Brilliant.
          Our next stop of the day was the Shore Temple, which overlooked the Bay of Bengal. The two shrines that constitute this seaside temple are constructed of granite. Since the temple is subject to the sea breezes, weathering on the windward side of the temple is especially pronounced. Saltwater from the sea sometimes comes in contact with the walls of the temple. When the water evaporates, salt crystals precipitate, expand, and force the rock apart. The sea side of the temple was noticeably more weathered as a result of this combined mechanism of chemical and physical weathering. Inside the shrine dedicated to Vishnu, one could find a large basalt pillar , which was imported from the Deccan plateau in Andhra Pradesh. It looked like this specimen of igneous rock contained the darkly colored minerals amphibole and pyroxene. Apparently, this rock is used as a phallic symbol.
          Two of the other notable rock types that I observed in the area near the shore temple were laterite and charnockite. Laterite is a rock that is typically found in hot, tropical climates like southern India.This rock is rich in iron and aluminum and has a characteristic red color due to the presence of iron oxides. The process by which laterite is formed (laterization) occurs when intense chemical weathering underneath the parent rock leaches all of the major ions, leaving behind mostly iron and aluminum. As a result of its dense chemical composition, laterite is frequently used in India as a house building medium in the form of bricks. Charnockite is named after Job Charnock, who is the man who first discovered this rock. Charnockite is a metamorphic rock that is classified as an orthopyroxene granite. This darkly colored mafic rock contains the minerals amphipole, pyroxene, and plagioclase. I was surprised by the high specific gravity of this rock.
          After our last temple stop at the Shore Temple, we hopped back on the bus and made our way to the Dune Eco Resort. We enjoyed many types of  authentic Indian snacks including "good day" and "nice time" biscuits. In India, biscuit = cookie. Suresh pointed out some interesting land forms along the way including man-made pits designed to catch excess water from the ocean. When the water evaporates from the pits, salt is left behind as a useful precipitate. Upon our arrival at the Dune, we were welcomed with coconuts with straws and presented with flowery necklaces.