The Makkah Gate, or Baab Makkah, is a historic landmark in Jeddah, Saudi Arabia. Located at the beginning of the road leading to the holy city of Mecca, this magnificent gate has witnessed countless pilgrims embarking on their journey to the birthplace of the Prophet Muhammad. Its three arches and imposing towers have served as a welcoming entrance to Jeddah for centuries.
The construction of the Makkah Gate, along with many other historic buildings in Jeddah, is characterized by the extensive use of coral stone. Coral stone is a natural building material formed from the skeletons of marine organisms. It is abundant in the coastal regions of the Red Sea, including Jeddah.
The Formation of Coral Stone in Jeddah - A Geological Process
The formation of coral stone in the Jeddah region is a complex geological process that takes place over millions of years and is closely linked to the specific environmental conditions of the Red Sea.
Coral reefs as a foundation:
Biological construction: Corals are sessile marine invertebrates that live in colonies. They secrete a hard exoskeleton made of calcium carbonate (calcium and carbon dioxide) to protect themselves and form a solid structure. These skeletons form the basis for the formation of coral reefs.
Reef construction: Over long periods of time, coral reefs grow by continuously depositing new skeletons and linking with other organisms such as algae and other invertebrates.
Environmental conditions for reef formation:
Warm water: Corals thrive best in warm, tropical waters with temperatures between 23 and 29 °C.
Good light: Corals need sufficient sunlight for the photosynthesis of their symbiotic algae.
Clear water: High sediment concentrations can reduce light transmission and hinder coral growth.
Low nutrient input: Too high nutrient concentrations can lead to algal blooms that damage corals.
From coral reefs to coral stone:
When corals die, their calcareous skeletons remain. These skeletons are covered by the deposition of sediments such as coral rubble, mussel shells and other organic materials.
Diagenetic processes take place under the pressure of the overlying sediments and at elevated temperatures. The loose sediments are bonded together and solidified by cementation (precipitation of minerals).
Tectonic processes can raise the sea floor, causing the former coral reefs to rise above sea level.
Fossils in coral stone - time capsules from the past
Coral stone is not only an impressive building material, but also a window into the past. Numerous fossils can be found in the pores and layers of this rock. These fossilized remains of marine organisms that once lived in the coral reefs provide valuable insights into the development of life and the environmental conditions of past times.
Fossils of the following are often found in coral stone:
• Small organisms: mussels, snails, sea urchins and other small sea creatures that have become trapped in the cavities of the coral stone.
• Pieces of coral: fragments of other types of coral that have been baked into the surrounding material over time.
• Microfossils: Tiny organisms such as foraminifera or diatoms that are barely visible to the naked eye but can be found in large quantities in rocks.
The study of these fossils allows paleontologists to draw conclusions about the water temperature, salinity, depth and biodiversity of the seas of that time. They can also provide clues about climatic changes and tectonic processes that led to the formation and change of coral reefs.
Properties of coral stone:
Porous: Coral stone has a porous structure that is created by the numerous cavities of the former coral skeletons.
Rich in calcium carbonate: The main component of coral stone is calcium carbonate, which gives it great hardness and good resistance to pressure.
Decorative: The characteristic grain and the diverse colors make coral stone a popular building material.
Coral stone in Jeddah:
The Jeddah region was characterized by coral reefs for millions of years. The geological processes mentioned above resulted in a large amount of high-quality coral stone, which has been used as a building material for centuries. The porous structure of the stone ensures good thermal insulation, which is particularly important in hot climates.
Task:
At the gate You will find 2 different types of stone. One is limestone and the other is coral stone.
1. Compare the two stones in terms of color, structure, surface and enclosed fossils.
2. Consider which of these stones is more stable and which has better thermal insulation and state your reasons for this.
3. Find a place where the two types of stone were used next to each other and send me a photo along with your answers.
