Why is this the answer?

The answer is pearl because this special riddle gives us wonderful clues about a natural treasure found deep in the ocean. A pearl is a beautiful, shiny jewel, and all the clues in the poem tell us exactly what it is like and where it comes from. Let us look at the first part of the riddle: "Lovely and round." This is the perfect way to describe a pearl's shape. Pearls are usually shaped like little spheres or balls, which makes them easy to string together for necklaces or earrings. Sometimes they are not perfectly round, but they always have a pleasing, smooth shape. Next, the riddle says, "I shine with pale light." This describes a pearl's special, soft glow. Pearls do not sparkle brightly like a diamond or a piece of glass. Instead, they have a gentle, beautiful shine called luster. This pale light is what makes pearls so elegant and unique when someone wears them. Now for the cleverest part: "grown in the darkness." This clue is all about where a pearl is born. A pearl grows inside a creature called an oyster or a clam. These creatures live deep down on the bottom of the ocean, where there is not much sunlight. It is very dark inside the oyster's shell, like a tiny secret cave. The pearl forms when a small piece of sand or an irritant gets inside the shell. The oyster slowly covers that tiny piece with many, many layers of a smooth, glowing material called nacre. It takes many years for the pearl to slowly "grow" this way, all in the darkness of the shell and the deep ocean water, until it is a perfect size. Finally, the riddle says, "a lady's delight." This is because pearls are used to make some of the prettiest and most classic jewelry in the world. For a long time, pearls were very expensive and only worn by kings, queens, and wealthy people. Today, many people love to wear pearl necklaces, bracelets, and earrings. They are considered very special gifts and bring joy to those who wear them. All these clues together show that the mysterious, round, and pale-shining object grown in the darkness can only be a pearl.