What is Marble?
Marble is a rock that is composed mostly of calcite. The forces of heat and pressure create this metamorphic rock. Typically, limestone (a sedimentary rock) becomes re-crystallized in the metamorphism process. Marble comes in many varieties, and based on the place where it was created, it can be considered foliated or non-foliated. As a result, it can contain many impurities like mica, gneiss, and phyllites.
Alabama Marble:
This monument contains a special type of marble only found in the central portion of the state of Alabama. Alabama marble contains >95% calcite, a mineral that appears white in color. It also contains calcium carbonate, a distinctive compound found in most marbles. The town of Sylacauga is where the purist deposits of this type of marble are found. They contain the least amounts of foliation and the presence of impurities (like clay, chert, and sand). The Sylacauga marble deposit is in dark red on the map below.
Foliated vs. Non-foliated Rock:
Foliated metamorphic rocks are layered. This reflects the direction that pressure was applied to the rock when it was metamorphosed. The mineral grains align, creating a plate/layer-like appearance. Gneiss and slate are common types.
Non-foliated rocks occur due to heat and pressure being applied in many directions. A sheet-like appearance does not occur as minerals are not specifically arranged.
Logging Tasks:
- Observe the marble monument. Describe the texture, appearance, and crystal size of this rock.
- Is this specimen of marble foliated or non-foliated?
- Note the color variations in the rock. Are there any veins/impurities found in the rock? If so, what is the color of this portion of rock?
- 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://www.britannica.com/science/marble-rock
https://www.thoughtco.com/marble-rock-geology-properties-4169367
https://yellowhammernews.com/why-sylacauga-marble-is-known-around-the-world/
https://geology.com/rocks/metamorphic-rocks.shtml
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