This earthcache brings you to a glacial erratic consisting of garnet-mica schist that was transported to Indiana in a giant sheet of ice. Garnet-mica schist is a metamorphic rock defined by its mineralogical composition. The flat, wavy minerals are the mica and the larger red minerals are the garnets.
Schists form as a result of regional metamorphism as igneous or sedimentary rocks undergo increasing pressure and temperature during mountain forming and other tectonic processes. Shale is a common parent rock of garnet-mica schist, the different kinds of clays in the shale recrystallizing to form the silicate minerals (among them garnet and mica) in the schist.
Email or message me the answers to the following questions to qualify for this cache:
1) Approximately how much of this rock is made up of garnets?
2) What is the average size of the garnets? What is the range of sizes present?
3) Do you think these garnets are gem-quality? Why or why not?
Garnets as Minerals
Garnet is a family of minerals having similar physical and crystalline properties. They all have the same general chemical formula, A3B2(SiO4)3, where A can be calcium, magnesium, ferrous iron, or manganese, and B can be aluminum, ferric iron, or chromium, or in rare instances, titanium.
Industrial Uses of Garnets
The first industrial use of garnet appears to have been as coated sandpaper manufactured in the United States by Henry Hudson Barton (founder of Barton Mines Corp.) in 1878. Its use has grown from that single sample of garnet coated sandpaper, to world industrial uses of more than 110,000 tons per year. In 1994, United States production of industrial garnet was valued at about $14 million, while gem garnet production was valued at only about $233,000.
Garnets in Pop Culture
Garnet is the January birthstone, and pure examples of garnets are commonly used as gemstones. They were very popular decorative gemstones and inlays during the Iron Age in Europe and remain popular among gemstone and mineral collectors. Also, they are pretty.
Primary source:
http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/garnet.html