This page has information about the Mineral and Rock Collection bags handed out at the 2021 Chicagoland Gems & Minerals Association show.
“May the quartz be with you!” is the theme of this year’s Chicagoland Gems & Minerals Show. Four of the six minerals and rocks in your Kids Corner collection are varieties of quartz.
Each collection bag includes one or more small, elongated quartz crystals. Some of these crystals are double-terminated, which means that they have well-formed crystal faces at both ends. These crystals were collected on Madagascar, a large island off the west coast of Africa.
Here’s a good online reference about the mineral quartz and its many uses: https://geology.com/minerals/quartz.shtml This article includes detailed lists of the many varieties of quartz: http://www.quartzpage.de/gen_types.html
Citrine (tumbled crystals)
Yellowish quartz is called citrine. The yellow color usually comes from iron minerals included within the crystal. The citrine specimens in the collection bags are pieces of yellowish-to-milky-to-clear quartz that have been run through a rock tumbler to make them rounded and polished.
Naturally formed citrine is pretty rare. Much of the yellow quartz sold today is formed by heating amethyst. This web page has detailed information about how citrine and how it forms: https://geology.com/gemstones/citrine/
Amethyst (rough and broken crystals)
Purple-colored quartz crystals are called amethyst. The collection bags include amethyst from the famous amethyst geode mines in Brazil. Some pieces are broken amethyst crystals, others are masses of small crystals that may include some white or clear quartz along with the purple amethyst. These amethyst pieces were produced when large amethyst geodes were broken out of the rock where they formed, or when larger geodes were broken open the reveal the crystals inside.
Like citrine, amethyst crystals include iron atoms within the crystal matrix. However, in amethyst, the iron has been hit by low-level gamma radiation, which produces the purple color.
Go here to read more about amethyst: https://geology.com/gemstones/amethyst/ This Scientific American blog post includes historical and scientific information about amethyst, including how it gets its purple color: https://blogs.scientificamerican.com/rosetta-stones/the-origin-of-amethysts-may-leave-you-tingly/ Here’s a link to a long article about amethyst mining in Brazil: https://www.gia.edu/doc/Amethyst-Mining-in-Brazil.pdf
Agate is one of the cryptocrystalline (“hidden crystals”) varieties of quartz, where the crystals are much too small to see, even with a microscope. Agates usually have very narrow bands of color or texture, which help distinguish them from other cryptocrystalline types of quartz, like jasper or chalcedony.
Go here to learn more about the many varieties of agate: https://geology.com/gemstones/agate/
The agates in the collection bag are almost all Lake Superior Agates, a variety of agate found in Minnesota and the Upper Peninsula of Michigan. Go here to learn more about Lake Superior Agates: http://www.geologyin.com/2017/06/where-and-how-to-find-lake-superior.html
Fluorite (cleavage crystals
Fluorite crystals break to form flat surfaces in four different directions (a property called perfect cleavage). The resulting cleavage fragments may be shaped like a triangle or an octahedron (a shape with eight triangular faces). Fluorite is often purple in color, but it can also be yellowish, green, or clear. Your collection bag may include more than one piece of fluorite; if so, they will probably be different shapes and colors.
Go here to read more about fluorite and its many uses: https://geology.com/minerals/fluorite.shtml Fluorite is the state mineral of Illinois: https://isgs.illinois.edu/outreach/geology-resources/fluorite-illinois-state-mineral Many of the fluorite specimens in the collection bags came from the famous Cave-in-Rock mines in far southern Illinois. Go here to read more about Cave-in-Rock fluorite: https://www.treasuremountainmining.com/index.php?route=pavblog/blog&id=94
Apache Tears (Obsidian)
Apache tears are rounded lumps of black volcanic glass (obsidian) that form within certain types of lava flows. Your collection bag includes at least two specimens, one with traces of pale gray weathered rock coating the surface and one that has been polished smooth and shiny in a rock tumbler.
Go here to learn more about Apache tears: https://en.wikipedia.org/wiki/Apache_tears This page tells the story behind the name, Apache tears: https://www.firstpeople.us/FP-Html-Legends/Apache_Tear_Drop-Apache.html