Metamorphic Rocks: 3 Examples

We encounter rocks everywhere, especially in the country. But, how much do we know about them? To us, they are just static elements of nature. Are rocks still as they seem to be? In fact, rocks move and change as they are subjected to a dynamic cycle taking place between three types of rocks: Sedimentary, igneous, and metamorphic. Sedimentary rocks are formed by the deposition of rock fragments on the surface of the Earth. Igneous rocks, on the other hand, come into being by the cooling and hardening processes of lava. Metamorphic rocks, of which the parent rock is any of the three types, are formed when the original rock is exposed to heat or pressure. The metamorphism that the rocks undergo is a fascinating subject. Here are just three examples of metamorphic rocks:

1.     Marble

Let’s look at first what limestone is as it is the parent rock of marble. Limestone is a sedimentary rock that is formed by the deposition and compression of marine shells on the sea bed. It was widely used as a building material by many antique civilizations in the past. If you visit ancient Greek or Roman cities, for example, you can see some standing buildings erected with the use of limestone blocks.

Photo: An example of a wall built in limestone blocks

When limestone is exposed to heat and pressure, it transforms into marble. Marble had a significant role in ancient construction as its parent rock. Besides, it has been admired as a sculpture material.

Photo: The marble statue “David” by Michelangelo

2.     Slate

Slate is a fine-grained metamorphic rock. Its parent rock is shale, a sedimentary rock that is mostly composed of clay and quartz. Being rich in clay makes this rock an important material in ceramic production. The ones with a high amount of organic material, on the other hand, are called oil slates and can produce oil.

Photo: Shale fragments

Slate is mainly composed of mica, chlorite, and quartz. Depending on the presence and amount of other contents such as iron sulfide and hematite, it can be found in a variety of colors: black, blue, purple, etc. One of its main uses is roofing and flooring.

Photo: Slate roof tiles

3.     Gneiss

Before diving into gneiss, let’s look at its parent rock. Granite, an igneous rock formed beneath the Earth’s surface by cooling extremely slowly, is mainly composed of feldspar and quartz and is used in road paving as well as building.

Photo: Granite

When granite is subjected to high heat and pressure due to tectonic activities, metamorphism took place and gneiss is formed. Through this transformation, the grain size decreases and the mineral structures line up, which leads to a banded appearance. It is commonly used as a road building material. When crushed, gneiss is utilized in construction sites and landscape design too. Polishing the material adds a decorative aspect to gneiss and makes it a useful stone for several architectural elements such as floor tiles and window sills.

Photo: Gneiss

References:

“Gneiss.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/gneiss. 

“Granite.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/granite. 

“Limestone.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/limestone. 

“Marble.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/marble-rock. 

“Rock.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/rock-geology. 

“Shale.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/shale. 

“Slate.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/slate-geology.