Enroute to the Meadow
The Campus Schist is shown on the images on this page.
The most distictive feature of this rock is its foliation, which is
formed by
the alignment of sheet-like mica grains. The foliation causes the rock to
cleave along the horizontal planes, as seen on the photograph to the
left. Two kinds of mica occur in these rocks -- muscovite and biotite --
along with quartz and plagioclase feldspar. At several localities the
altered remains
of garnet are present as well. A
closer look shows some of the minerals and structure of this rock.The
red is remnant garnet, the black is biotite, and the light colored
material is a mixture of muscovite, quartz, and plagioclase. This mineral
assemblage --
mica-plagioclase+/-garnet is diagnostic of an aluminum-rich sedimentary
protolith.
The protolith is the kind of rock present before metamorphism.
In this case, it was probably an Al-rich mudstone or sandstone. The
sedimentary environment could have been a delta, mudflat, or
lagoon like the one at
Natural Bridges;
anywhere that fine-grained sediments or muds accumulate. The Al in
the clay minerals in a sedimentary rock get metamoprphosed into the micas
and/or garnets of this metamorphic rock. Most of the schist on campus is
deeply weathered. The iron in the biotite has turned to oxidized minerals
such as goethite and limonite, giving this rock its rusty brown color.
Fresh schist, as can be observed in Cave Gulch, is steel grey to black in
color. Good outcrops of weathered schist, showing the structure of the rock,
exist in the roadcut on
Steinhart Way between the Bay Tree Bookstore and the East Field House.
I am gladly accepting better photographs of these rocks!
All photographs by
Kenta Williams 1995
The protolith is the kind of rock present before metamorphism.
In this case, it was probably an Al-rich mudstone or sandstone. The
sedimentary environment could have been a delta, mudflat, or
lagoon like the one at
Natural Bridges;
anywhere that fine-grained sediments or muds accumulate. The Al in
the clay minerals in a sedimentary rock get metamoprphosed into the micas
and/or garnets of this metamorphic rock. Most of the schist on campus is
deeply weathered. The iron in the biotite has turned to oxidized minerals
such as goethite and limonite, giving this rock its rusty brown color.
Fresh schist, as can be observed in Cave Gulch, is steel grey to black in
color. Good outcrops of weathered schist, showing the structure of the rock,
exist in the roadcut on
Steinhart Way between the Bay Tree Bookstore and the East Field House.
I am gladly accepting better photographs of these rocks!