This is an earthcache with no physical container to find. This earthcache is located at the heart of downtown Kirksville at the Adair County Courthouse. The primary goal of this earthcache is to highlight the granite colonettes outside of each of the four courthouse entrances. The doors the gps coordinates should take you to is no longer used for everyday entrance to the courthouse. Since Covid, only one entrance is open for everyday use, which is the entrance on the west side of the courthouse, however, you do not need to enter the courthouse to complete this earthcache so that should not be an issue.
The Adair County Courthouse is open from 8:30am to 4:30pm daily, minus weekends and holidays, of course.
There are three classes of rock and they are as follows:
1. Igneous- formed when molten rock cools and solidifies
2. Metamorphic- formed when existing rocks, like igneous or sedimentary rocks, are significantly changed by intense heat and pressure
3. Sedimentary- Sedimentary rocks are formed when weathered particles from pre-existing rocks, or pieces of once-living organisms, accumulate on the Earth's surface, are transported by water, wind, or ice, and then settle and become compacted and cemented together, a process called lithification.
All three classes of rock can be found naturally in Missouri. Today we are focusing on a type of igneous rock- granite. Specifically, we are going to focus on the formation of granite, how it gets it various colors, and its mineral composition.
Igneous rocks can be divided into two main types: Extrusive or Intrusive.
Extrusive igneous rocks (volcanic rocks) are formed from rapidly cooling lava on the earth’s surface. Extrusive rocks have a fine grained or glassy surface because the rapid cooling prevents the crystals from becoming larger. Extrusive rocks are typically less dense than intrusive because gas bubble that occur during the rapid cooling, and the smaller crystal size within the rocks. Common examples are basalt, rhyolite, and andesite.
Intrusive igneous rocks form under the earth’s surface through a slow process of magma cooling that can take thousands or millions of years. This slow cooling process allows for the crystals to grow larger, making them visible to the naked eye and giving the rock a coarse texture. Intrusive igneous rocks are also typically more dense than extrusive. Common examples are, granite, gabbro, and diorite
Granite, as evidenced by its large, visible crystals, is an intrusive type of igneous rock. This means it it is made by slow cooling magma beneath the earth’s surface.
Granite comes in a variety of colors. These various colors are caused by different mineral composition within the granite. A higher rate of certain minerals causes the granite to take on certain colors. See the chart below.
As the chart shows, if the granite has a higher concentration of biotite, it will be a more black or dark brown color. If it has a higher concentration of feldspar, it will be a off-white color. And if the granite has a higher concentration of potassium feldspar, it will have a pinkish tint to its color.
In order to log a find and claim the 🙂 for this earth cache, you are required to complete/answer the following:
- What class of rock is granite?
- What color in the granite colonettes stands out most to you? What does this mean about its mineral composition?
- Is granite an intrusive rock or an extrusive rock? How can you tell by looking at it?
- Post a photograph of yourself (face not required) or a personal item at the site.
Thanks for completing this earth cache, and I hope you enjoyed it. In order to get the most accurate information I could, I used www.geologyin.com, and Association of American State Geologists.
Bonus rock joke: You know the old saying—igneous is bliss.