Orbicular Diorite - Menlo Park, California
Posted by: Groundspeak Premium Member Volcanoguy
N 37° 27.319 W 122° 10.216
10S E 573384 N 4145707
Orbicular diorite block at the USGS Campus in Menlo Park, California.
Waymark Code: WMADH0
Location: California, United States
Date Posted: 12/31/2010
Published By:Groundspeak Regular Member lenron
Views: 3

This orbicular diorite block is one example of a series of large blocks of rocks from various locations, which are on display around the USGS Campus in Menlo Park. There is a self-guided tour of the campus available at the visitor center.
Text of Sign: “This two and one-half ton block of orbicular diorite, from the southern Sierra Nevada, crystallized 100 million years ago. The orbicular structures formed within a vertical pipe which conducted hot magmatic fluids, with suspended rock fragments, along the margins of a cooling granitic intrusion. The rock fragments served as nuclei which became coated with minerals which precipitated out of the magmatic fluid. Eventually, multiple mineral layering created spherical shapes. Note that the irregular shapes are usually closely-packed and touch one another; areas where there are apparently no orbicules, are generally occupied by inconspicuous unrimmed fragments.”

Type of Display: Geological

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Volcanoguy visited Orbicular Diorite - Menlo Park, California 12/15/2010 Volcanoguy visited it