Manhattan Schist

In the first part of yesterday’s post, Oh, Schist!, I mentioned that schist’s alignment of platy minerals created planes of weakness in the rock, but that in some cases, schist can be a very strong rock. Meet the Manhattan schist.

The Manhattan schist formed from mud deposited on the ocean floor and scraped in continental collisions during the formation of Pangaea over 450 - 300 million years ago. These collisions, part of the Taconic Orogeny, created a mountain chain taller than the Himalayas, and squeezed and baked the rocks under high pressure and temperature forming the Manhattan schist. In New York, you can build very high skyscrapers on the Manhattan schist.

Why is the Manhattan schist so strong? It has to do with the mineralogy and the internal structure. The unit is characterized by a lack of internal layering, the presence of tough black amphibole, and of wear-resistant garnet, kyanite, and sillimanite. The last two minerals are metamorphic grade index minerals, and indicate the Manhattan schist was exposed to very high pressure and temperature.

Enjoy this outcrop of the folded and scraped Manhattan schist in Central Park, Manhattan from: https://geologypics.com/manhattan-schist-and-skyscrapers-of-ny-city/ by @MarliMiller

#ManhattanSchist #TaconicOrogeny #rocks #geology #ScienceMastodon