Coral is a marine animal that belongs to the class Anthozoa and the phylum Cnidaria. It is composed of small, soft-bodied animals called polyps that secrete a hard, calcium carbonate skeleton. Coral is found in warm, shallow waters around the world, and is known for its bright, vibrant colors and unique patterns. While coral is not considered a mineral, it has been used for decorative and ornamental purposes for centuries, and is often classified as a precious or semi-precious gemstone. Coral jewelry and ornaments are popular in many cultures, and are often associated with good luck, protection, and healing properties. However, the harvesting of coral for commercial purposes has had a significant impact on coral populations around the world, and many species are now considered endangered or threatened due to overexploitation and habitat loss.

According to Greek legends, coral is the blood spilled by the hero Perseus when he cut off the head of the monster Medusa. In fact, coral is skeletal material produced by marine animals. Coral is organic and created by living organisms. When coral polyps die, the hardened skeleton remains and this material is used as a gemstone. Most corals are white, but nature can create coral in many other colors, including the popular orange to red forms. Usually its compound is calcium carbonate. Corals have a dull appearance when collected and are then polished. Precious corals, which are red and pink in color, are found around Japan and Malaysia in African coastal waters and the Mediterranean. Black corals are mined from around the West Indies, Australia and Pacific Islands.

Coral is a gemstone that has been used for thousands of years. Besides the beautiful solid colors found in Coral, there may also be color zones or swirls where white, pink, orange and red are most common.

Coral gemstones can be solid or porous depending on polyp formation. Despite Coral’s beautiful colors, it is very soft and brittle and does not make a durable gemstone. It is prone to both scratching and chipping.

Mineral Group: Organic Minerals

Mineralogy: Mostly calcium carbonate (CaCO3)

Environment: Corals are primitive animals belonging to the Phylum Coelenterata or Cnidaria and are found anywhere in the world’s ocean at depths ranging from the tidal mark to the abyss, up to 6000 m.

Coral Varieties

  • Black Coral: Black colored marine coral species from the Antipatharia family.
  • Precious Coral: Also known as Red Coral. Precious Coral has a natural pink to red color and is Coral’s most desirable form of jewellery.
  • Red Coral: The marine coral species corallium rubrum (or several related species) with a natural color from light pink to deep red.

Geological formation of coral

Coral is formed by small animals known as coral polyps, which belong to the class Anthozoa of the phylum Cnidaria. These tiny organisms secrete a hard, calcareous skeleton made of calcium carbonate that serves as their protective home. Over time, as individual polyps die and new ones take their place, the calcareous skeleton grows and forms large, complex structures known as coral reefs.

Coral reefs are typically found in warm, shallow waters in tropical and subtropical regions around the world. They are formed by the accumulation of coral skeletons and other calcareous material over many thousands of years. The growth rate of coral reefs can vary depending on environmental factors such as water temperature, water quality, and the availability of nutrients.

Coral reefs play an important role in the marine ecosystem, providing habitat and shelter for a wide variety of marine life, including fish, crustaceans, and other invertebrates. They also protect coastlines from erosion and storm damage, and are a popular destination for tourism and recreation. However, coral reefs are under threat from a range of factors, including climate change, pollution, overfishing, and habitat destruction.

Coral reefs and their importance

Coral reefs are incredibly important ecosystems that support a vast array of marine life, including fish, invertebrates, and other organisms. They also provide a range of valuable ecological services, such as shoreline protection, nutrient cycling, and carbon sequestration. Here are some of the key reasons why coral reefs are important:

  1. Biodiversity: Coral reefs are one of the most diverse ecosystems on Earth, supporting an estimated 25% of all marine species, despite covering less than 1% of the ocean floor. Many of these species are dependent on coral reefs for their survival, including commercially important fish and shellfish.
  2. Fisheries: Coral reefs provide a critical source of food and income for millions of people around the world. They support some of the world’s most important fisheries, including those for tuna, snapper, and grouper, as well as for many types of shellfish.
  3. Coastal protection: Coral reefs act as natural breakwaters, protecting coastlines from storm surges, waves, and erosion. This is particularly important in areas where sea level rise and increased storm frequency and intensity due to climate change are becoming more common.
  4. Tourism: Coral reefs are a major attraction for tourists, generating billions of dollars in revenue each year. They are particularly popular for activities such as snorkeling and scuba diving, and their beauty and diversity are a major draw for travelers.
  5. Climate regulation: Coral reefs play an important role in regulating the Earth’s climate by absorbing and storing large amounts of carbon dioxide from the atmosphere. This helps to mitigate the impacts of climate change and ocean acidification.

Overall, coral reefs are a vital part of the marine ecosystem and provide a wide range of benefits to human societies. Protecting and preserving these ecosystems is essential for the health and well-being of both marine and human communities around the world.

Physical Properties

Coral is a marine organism that belongs to the family of Anthozoa, and it has certain physical properties that distinguish it from other gemstones. Here are some of the physical properties of coral:

  1. Hardness: Coral has a hardness of 3.5 on the Mohs scale, which makes it relatively soft compared to other gemstones. As a result, it can be easily scratched or damaged, and it requires special care when cleaning or handling.
  2. Density: The density of coral ranges from 1.5 to 1.7 g/cm³, which makes it fairly lightweight compared to other gemstones. This makes it comfortable to wear as jewelry, but it also makes it susceptible to damage from impacts or pressure.
  3. Color: Coral can come in a wide range of colors, including white, pink, red, orange, and black. The color of coral is determined by the presence of pigments and other organic compounds, as well as by the species of coral from which it is derived.
  4. Luster: Coral has a dull to waxy luster, which is characteristic of organic materials. This is different from the glassy or metallic luster of many other gemstones.
  5. Transparency: Coral is opaque, which means that light cannot pass through it. This is because it is made up of numerous small calcium carbonate structures called polyps, which are densely packed together.
  6. Refractive index: The refractive index of coral ranges from 1.486 to 1.658, depending on the species and color of the coral. This determines how light is bent and reflected within the gemstone, and can affect its appearance and beauty.

Overall, coral is a unique and beautiful gemstone that has its own distinct physical properties. Its softness and susceptibility to damage make it important to handle with care, but its beauty and cultural significance make it a popular choice for jewelry and decorative objects.

Uses of coral

Coral has been used for a wide range of purposes throughout human history, from decorative objects to medicinal remedies. Here are some of the most common uses of coral:

  1. Jewelry: Coral is a popular choice for jewelry, particularly in traditional and ethnic designs. It is often carved into beads, pendants, and other shapes, and can be combined with other gemstones and metals to create unique pieces.
  2. Decorative objects: Coral has long been used to create decorative objects, such as sculptures, figurines, and ornaments. Its unique color and texture make it a popular choice for home decor and other decorative applications.
  3. Feng shui: In the practice of feng shui, coral is believed to bring positive energy and luck into the home. It is often used in decor and jewelry to promote good fortune and prosperity.
  4. Aquariums: Coral is also a popular choice for aquarium enthusiasts, as it can provide a natural and beautiful habitat for fish and other marine life.

It is worth noting that the use of coral for decorative purposes has led to overharvesting and damage to coral reefs. As such, it is important to ensure that any coral products you purchase are sustainably sourced and do not contribute to further harm to these fragile ecosystems.


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