Hello, I'm an expert in the field of gemology, and I'd be delighted to explain why a pearl is considered a gem rather than a mineral. The distinction between gemstones and minerals is based on several criteria, including their formation, structure, and the presence of organic processes. Step 1: English Explanation Gemstones are typically minerals, which are naturally occurring, inorganic solid substances with a distinctive crystal structure. They have a specific chemical composition and a crystalline form that can be identified under a microscope. This crystalline structure is one of the key characteristics that differentiate minerals from other types of stones. Pearls, on the other hand, are unique in the world of gemstones. They are formed by living organisms, specifically mollusks such as oysters, mussels, and clams. The process of pearl formation begins when an irritant, like a grain of sand or a small parasite, gets trapped inside the mollusk's shell. To protect itself, the mollusk secretes layers of a substance called nacre around the irritant. Over time, these layers build up and form a pearl. Nacre is a blend of calcium carbonate, which can take the form of aragonite or calcite, and it is what gives pearls their characteristic luster and iridescence. The key difference between nacre and a typical mineral is that nacre does not have a distinctive crystal structure. Minerals are defined by their internal arrangement of atoms, which is visible in their crystalline form. Since nacre lacks this atomic structure, it is not classified as a mineral. Furthermore, the formation of pearls is an organic process. They are created by living organisms as a byproduct of their defense mechanisms. This biological aspect of pearl formation is another reason why pearls are not considered minerals. Minerals, by definition, are inorganic and do not involve any biological processes in their formation. In the world of gemstones, pearls are highly valued for their beauty and rarity. They possess a unique luster and a soft, subtle color that is not found in typical minerals. The organic origin and the lack of a crystal structure are what set pearls apart from other gemstones and contribute to their classification as gems rather than minerals. Step 2: Divider read more >>

Gemstones are usually minerals. Pearls are deposits of calcium carbonate (aragonite, calcite, or both) called nacre. Pearl (nacre) is not a mineral because it does not have a distinctive crystal structure and because it is formed by the action of a living organism.read more >>