Tuesday, July 13, 2010

Manhattan garnet

One of the most impressive mineral specimens unearthed in New York City is the famous Kunz garnet (also called the sewer garnet or the subway garnet) discovered in 1885.  It's a massive 9 pound, 10 ounce almandine garnet, seven inches in diameter, dug up on West 35th Street near Broadway. 


Today the area looks like this:


Not a great site for mineral collecting anymore!

There are a number of conflicting stories about this garnet.  Different sources state that it was uncovered during the excavation of a sewer or a subway.  The oldest source, however, related by mineral collector and dealer John Betts, shows that it was apparently a sewer excavation.

From the 1886 New York Academy of Sciences Transactions (Vol. 5, pp. 264-266):

The finest large garnet crystal ever found, perhaps, in the United States, was discovered, strange though it may seem, in the midst of the solidly-built portion of New York City. It was brought to light by a laborer excavating for a sewer in West 35th Street, between Broadway and Seventh Avenue, in August, 1885. A quartzite vein, traversing the gneiss, contained the crystal.

The garnet eventually found its way into the hands of George F. Kunz (1856-1932), an emminant New York City mineralogist who described it to the New York Academy of Sciences (hence the name Kunz garnet).


Various sources state that this garnet was, for a time, used as a doorstop for the Department of Public Works in New York City but I've been unable to verify this anywhere. A good story if it's true!

Anyway, Kunz presented the garnet to the New York Mineralogical Club which later donated it to the American Museum of Natural History in Manhattan.  I believe it's on display in the New York City Minerals collection but I haven't been there in a few years.

Hundreds of spectacular mineral specimens have been discovered in the bedrock of Manhattan (primarily in the 19th century when a lot of the subway, skyscraper, and water tunnel excavations were going on).  The Kunz garnet was found in the Manhattan Formation (also called the Manhattan Schist), a rock unit which underlies much of the island and formed from the metamorphism of sedimentary rocks by a mountain-building event some 440 million years ago (Taconic Orogeny).

I'll write more about the Manhattan Formation another day.

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