Ya gotta love these scientific terms! Just what does Plagioclase Feldspar Phenocrysts actually mean?
Well, let's break it down:
Plagioclases is a group of feldspar made up of silicate minerals.
Feldspar is a family of silicate minerals crystallized from magma.
A Phenocryst is a conspicuous , large crystal embedded in a finer-grained matrix of smaller crystals in igneous rock.
So . . . when you put it all together, Plagioclase Feldspar Phenocrysts really means: silicate minerals crystallized from and embedded in magma which has cooled and hardened.
When you locate a rock with these crystals in the area, they will look like light colored, glassy, angular crystal grains in the darker basalt matrix. They were probably formed when the magma was still deep in the earth. In this area of Wisconsin, a rift which extends from the Lake Superior basin as far as Kansas to the southwest had volcanoes which erupted and molten lava flowed in the valleys producing layers of hard, dark-grey rock called basalt. (See GC5NEFD - IATCC - It’s Earth’s Fault)
IATCC is the cache designation to highlight a series of EarthCaches along the Ice Age National Scenic Trail grouped into a special category called "ColdCache."
The Ice Age Trail is one of eleven National Scenic Trails designated by the National Park Service. This unique trail is entirely within the state of Wisconsin and follows along the terminal moraine of the most recent glacier which retreated about 10,000 years ago.
This project is supported by the Ice Age Trail Alliance (IATA). The goal is to bring more visitors to the trail and promote public awareness, appreciation, and understanding of Wisconsin’s glacial landscape.
The IATA has created an awards program to encourage visits to the trail and ColdCache sites. This awards program is separate from, and in addition to, any other Geo- or EarthCache awards program.
A current list of approved ColdCache sites can be found on the “IATCC Bookmark List”. More information on the Ice Age Trail Atlas, the Companion Guide, the ColdCache Project and Awards Program can be found on the “ColdCache Webpage”.
DNR Permission
The Geocache Notification Form has been submitted to Kurt Dreger of the Wisconsin DNR. Geocaches placed on Wisconsin Department of Natural Resource managed lands require permission by means of a notification form. Please print out a paper copy of the notification form, fill in all required information, then submit it to the land manager. The DNR Notification form and land manager information can be obtained at: www.wi-geocaching.com/hiding
Resources
Encyclopedia Britannica
Geology of the Ice Age National Scenic Trail; by David M. Mickelson, Louis J. Mahler Jr., and Susan L. Simpson
Geology Walking Tour; Wisconsin Interstate Park; St. Croix Falls, Polk County, WI; by Ryan Peterson and Dr. William S. Cordua, University of Wisconsin - River Falls, Department of Geology
Roadside Geology of Wisconsin; by Robert H. Dott, Jr and John W. Attig
University of Minnesota's Mineral Pages
To claim this find:
1. Locate the rock at ground zero with some Plagioclase Feldspar Phenocrysts. Describe the size and shape of the rock and the crystals embedded within it.