In Surah Ar-Rahman (55:22), the Quran declares: "From both of them emerge pearl and coral" (يَخْرُجُ مِنْهُمَا اللُّؤْلُؤُ وَالْمَرْجَانُ).
This verse mentions two marine treasures: the pearl (اللُّؤْلُؤُ) and coral (الْمَرْجَانُ). Modern science has revealed the fascinating nature of these two marine productions.
The pearl: a biological production
The pearl is produced by certain bivalve mollusks (pearl oysters, notably of the genus Pinctada). When a foreign body (grain of sand, parasite) enters the shell, the mollusk secretes layers of nacre (calcium carbonate in the form of aragonite and conchiolin) around the irritant. After several years, a pearl forms.
Natural pearls are rare: it is estimated that only one oyster in about 10,000 produces a gem-quality pearl.
Coral: a colonial animal
Coral is not a plant but a colonial animal belonging to the phylum Cnidaria (class Anthozoa). Each coral polyp secretes a skeleton of calcium carbonate (calcite or aragonite). Coral reefs are among the richest and most diverse ecosystems on the planet.
Red coral (Corallium rubrum) from the Mediterranean has been prized in jewelry since antiquity.
A remarkable knowledge
The fact that the Quran mentions these two marine productions as emerging "from both of them" (the fresh and salty seas mentioned in the previous verse) is remarkable. In reality, pearls and coral are found mainly in salty waters.
The biological nature of pearls and coral was only understood with the development of marine biology in the 19th and 20th centuries.