Limestone in Kentucky:
More than 50 percent of the surface rocks in Kentucky are limestone. Limestone is chiefly composed of the mineral calcite but can contain trace amounts of clay, silt, chert, and dolomite. Limestone is a sedimentary rock that can appear layered and contain fossils of shellfish and other animals. Kentucky was once covered by shallow seas that were a source for depositing sediment and marine debris. Over millions of years, limestone formed through lithification or the process of cementation and compaction of sediment into rock. Limestones are shades of bluish-gray to tan. Iron oxide impurities usually cause the brown, tan, and yellow shades, and the dark gray to black colors are caused by organic material. The texture of limestone ranges from coarse to very fine-grained.
Calcite Crystals in Limestone:
Calcite is present in Kentucky limestone as crystals or fossil fragments. Calcite can form from waters rich in calcium. As concentrations increase or the amount of water decreases, crystals of solid calcite crystals grow. Calcite crystals form in a hexagonal form and appear clear white in color. Geochemically speaking, calcite is composed of calcium, carbon, and oxygen atoms, forming the compound calcium carbonate. When calcite crystals become embedded in limestone, they are considered by geologists to be nodules.
What is Weathering?
Mechanical weathering is the process of wearing down rocks through physical processes. Wind, ice, and salt can act as wedges and help break rocks into fragments. Temperature fluctuations like cool nights and hot days always cause rocks to expand and contract, allowing for mechanical weathering. Evidence of mechanical weathering can be seen through hole-like divots in sedimentary rock (known as tafoni).
Chemical weathering refers to how chemical reactions change the composition of the rock, often wearing away a rock’s surface. Acid rain dissolves rock that contains calcium carbonate, while oxidation can weaken rock that contains iron.
Biological weathering is the effect that plants and animals have on weathering processes. Roots from plants can exert pressure on bedrock and crack it. Lichens and moss can deteriorate a rock face.
Logging Tasks:
- At the GZ, you should notice a memorial of limestone. Examine the boulder and note the appearance and color of the limestone. Based on the color of the rock at the GZ, what impurities are present in this specimen of limestone?
- What type of weathering (mechanical, chemical, or biological) seems to be affecting the rock at the GZ? Explain why you think this.
- Look on the backside of the boulder. You should notice a large nodule of calcite embedded in the rock. What is the width of this nodule?
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://igws.indiana.edu/RocksAndMinerals/Calcite#:~:text=The%20most%20common%20is%20as,of%20solid%20calcite%20crystals%20form
https://www.uky.edu/KGS/rocksmineral/rm-rocks-limestone.php
https://www.geologypage.com/2016/05/weathering.html
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